JP2019214717A - Inkjet magenta ink, ink set, and printed matter production method using said inkjet magenta ink and ink set - Google Patents

Abstract

To provide an inkjet magenta ink that makes it possible to obtain a high quality image that is free from a white patch and a mixed-color blur and has high color development, high clarity and high color reproducibility, and is also excellent in storage stability, discharge stability, and dryability, and an ink set containing the magenta ink.SOLUTION: The present invention pertains to an inkjet magenta ink comprising two or more types of pigments, a water-soluble organic solvent (A), a surfactant, and water, wherein: the two or more types of pigments include an azo pigment; the content of the azo pigment accounts for 0.5-8 mass% of a total amount of the magenta ink and for 35-100 mass% of the total amount of the pigments; the water-soluble organic solvent (A) contains a specific diol-based solvent (A-1) in an amount 5-250 times that of the contained molar quantity of the azo pigment; and the content of a cyclic amide-based solvent in the water-soluble organic solvent (A) accounts for at most 4.5 mass% of the total amount of the magenta ink.SELECTED DRAWING: None

Description

  An embodiment of the present invention relates to a magenta ink for inkjet, an ink set including the magenta ink, and a method for producing a printed material using the same.

  Since digital printing does not require a plate unlike conventional offset printing or gravure printing, it can be used in a wide variety of applications because it is possible to reduce production costs and reduce the size of a printing machine by small lot printing.

  There are two digital printing technologies currently used in the market. One type is called an electrophotographic system, which uses a powder or liquid toner to perform printing, and is a technology widely used in color printers, office multifunction peripherals, and the like. Another digital printing technology is the ink jet method, which is also used for various purposes, including consumer printers.

  The ink jet system is a recording system in which ink droplets are directly ejected from a very fine nozzle onto a printing substrate and adhered to obtain characters and / or images. It is an excellent printing technique that not only has the advantages of low noise of the device used and good operability, but also easy colorization.

  In addition to the features of the ink jet system, it can use many kinds of inks such as water-based ink, oil-based ink, solvent-based ink, and UV-curable (UV) ink, and can print on various printing base materials without contact. There is. Since printing can be performed on materials other than the paper base material, it is expected to be expanded to various applications including not only commercial printing applications but also sign / display printing applications.

  For example, in sign / display applications, printing machines that can print on a plastic substrate such as a polyvinyl chloride sheet or a PET film using a solvent-based ink or a UV ink have actually been marketed. However, in recent years, demands for water-based inks have been increasing in consideration of safety and environmental considerations.

  In order to respond to these demands, regardless of the base material used, printed matter having high color development (high density), high clarity (high saturation), and high color reproducibility and excellent image quality is required. The resulting aqueous ink is required. Above all, various studies have been made on magenta inks, which have a strong demand for their realization, as in Patent Documents 1 to 4. However, all of these were mainly intended for easily absorbable base materials such as plain paper or special paper.

  In recent years, with the expectation of further expanding the application of the ink jet system, the need for direct printing on hard-to-absorbable base materials such as art paper, coated paper, or lightly coated paper has been increasing. Therefore, it is required that a printed material having high color developability, high clarity, high color reproducibility, and high image quality can be produced for these substrates. However, the water-based ink has a high surface tension of water, does not easily penetrate into a poorly absorbable substrate, and is very hard to spread and spread. As a result, poor drying and / or white spots are likely to occur on the poorly absorbable substrate due to insufficient wetting and spreading of the aqueous ink. In addition, since the surface tension of the water-based ink is high, droplets coalesce on the substrate at the time of landing, which leads to deterioration in image quality such as uneven shading.

  Further, in order to achieve high color development, high sharpness, and high color reproducibility, selection of a coloring material to be used is also important. Generally, in a water-based magenta ink, a quinacridone pigment or an azo pigment is used as a coloring material (see also Patent Documents 2 to 4). However, quinacridone pigments have low coloring power and the color reproduction range is not sufficiently satisfactory. On the other hand, azo pigments have high coloring power and sharpness and a wide color reproduction range, but have poor stability to organic solvents and, in some cases, dissolve the pigment, and on the substrate, the original coloring property and / or sharpness of the pigment. There was a problem that the property could not be expressed. In addition, when an ink containing an azo pigment dissolved in an organic solvent is allowed to stand by for a long time in an ink jet head, the pigment is precipitated in a process in which water evaporates and the aqueous ink is concentrated, causing a problem such as nozzle clogging. Was.

  The present applicant has previously described in Patent Document 5 C.I. I. A water-based ink using Pigment Red 150 and a basic organic compound has been proposed. According to Patent Literature 5, it is possible to obtain an inkjet ink having excellent red color reproducibility and excellent ejection stability without causing a problem such as nozzle clogging.

JP-A-9-279070 JP-A-10-219166 JP 2005-29626 A JP 2007-99997 A JP 2014-214277 A

  Embodiments of the present invention have been made to solve the above-described problems, and an object of the present invention is to obtain a high-quality image having no white spots, high coloring and high sharpness regardless of the base material. Another object of the present invention is to provide a magenta ink for inkjet which is excellent in storage stability, ejection stability, and drying property, and a method for producing a printed material using the magenta ink.

  An object of another embodiment of the present invention is to provide an ink set including a magenta ink for inkjet, which can realize high color reproducibility even on a poorly absorbable base material and can obtain a high-quality image without color mixture bleeding. And a method for producing a printed material using the ink set.

  It is still another object of the present invention to provide a printed material having a poorly-absorbable substrate and having high color reproducibility and high quality images.

  As a result of intensive studies conducted by the present inventors to solve the above-described problems, two or more pigments including an azo pigment, and a diol-based solvent having a specific structure, and defining the amount of the diol-based solvent, The inventors have found that the above-mentioned problems can be solved by magenta ink for ink-jet, in which the amount of the cyclic amide-based solvent is not more than a certain amount, and an ink set containing the magenta ink for ink-jet, and have completed the present invention.

That is, an embodiment of the present invention is a magenta ink for inkjet containing two or more pigments, a water-soluble organic solvent (A), a surfactant, and water,
The two or more pigments contain an azo pigment,
The content of the azo pigment is 0.5 to 8% by mass based on the total amount of the magenta ink for inkjet, and 35 to 100% by mass based on the total amount of the pigment,
The water-soluble organic solvent (A) is a diol-based solvent represented by the following formula (1), wherein n is 1 and / or 2; Contains 5-250 times the amount of
In the water-soluble organic solvent (A), the diol-based solvent (A-2) in which n is 3 and / or 4 among the diol-based solvents represented by the following formula (1) is contained in the diol-based solvent. 0.1 times or less the molar amount of the solvent (A-1),
The present invention relates to a magenta ink for inkjet, wherein the content of the cyclic amide solvent in the water-soluble organic solvent (A) is 4.5% by mass or less based on the total amount of the magenta ink for inkjet.

HO- (AO) n-H (1)

(In the formula (1), AO represents an ethylene oxide group or a propylene oxide group, and n represents an integer of 1 to 4.)

  Further, an embodiment of the present invention relates to the magenta ink for inkjet, wherein the azo pigment includes a naphthol AS pigment and / or a β-oxynaphthoic acid-based lake pigment.

  In an embodiment of the present invention, the azo pigment includes a naphthol AS pigment, and a β-oxynaphthoic acid-based lake pigment, based on the total amount of the naphthol AS pigment and the β-oxynaphthoic acid-based lake pigment. The present invention relates to the magenta ink for inkjet, wherein the content of the β-oxynaphthoic acid-based lake pigment is 50 to 99% by mass.

  Further, in the embodiment of the present invention, the naphthol AS pigment may be C.I. I. The present invention relates to the above-described magenta ink for inkjet, including Pigment Red 150.

  Further, in the embodiment of the present invention, the β-oxynaphthoic acid-based lake pigment may be C.I. I. Pigment Red 48: 3.

  Further, an embodiment of the present invention relates to the magenta ink for inkjet, wherein the two or more types of pigments further include a quinacridone pigment and / or a solid solution pigment containing a quinacridone pigment.

In an embodiment of the present invention, the azo pigment includes a naphthol AS pigment,
The present invention relates to the magenta ink for inkjet, wherein the content of the azo pigment is more than 50% by mass and 99% by mass or less based on the total amount of the two or more types of pigments.

  Further, an embodiment of the present invention relates to the above-described magenta ink for inkjet, further comprising a binder resin, wherein the glass transition temperature (Tg) of the binder resin is 40 to 120 ° C.

  Further, an embodiment of the present invention relates to the above-described magenta ink for inkjet, wherein a spectral reflectance of a coated product having a wet film thickness of 6 μm and formed on a printing substrate is 10% or less in a wavelength region of 480 to 580 nm.

An embodiment of the present invention is an inkjet ink set including at least a cyan ink, a yellow ink, and a magenta ink,
The cyan ink and the yellow ink contain the diol-based solvent (A-1),
The present invention relates to an ink set, wherein the magenta ink is the magenta ink for inkjet.

  Further, in the embodiment of the present invention, the molar amount of the diol-based solvent (A-1) contained in each of the magenta ink, the cyan ink, and the yellow ink with respect to the molar amount of the azo pigment in the magenta ink. Is 5 to 250 times the amount of the above ink set.

  In addition, an embodiment of the present invention relates to a method for manufacturing an ink-jet printed matter, in which the magenta ink for ink-jet or the ink set is ejected from an ink-jet head, and ink droplets are attached to a poorly-absorbable substrate.

  Further, an embodiment of the present invention relates to the method for producing an ink-jet print, wherein the nozzle diameter of the ink-jet head is 10 to 30 μm.

  Further, an embodiment of the present invention relates to an ink-jet printed matter obtained by printing the above-mentioned magenta ink for ink-jet or the above-mentioned ink set on a poorly-absorbable substrate.

  According to the embodiment of the present invention, regardless of the substrate, there is no white spot, a high-quality image having high color development and high clarity can be obtained, and storage stability, ejection stability, and drying property are excellent. It has become possible to provide a magenta ink for inkjet and a method for producing a printed material using the magenta ink.

  Further, according to another embodiment of the present invention, even in a poorly absorbable substrate, it is possible to realize high color reproducibility, and to obtain a high-quality image without color mixture bleeding, an ink set including magenta ink for inkjet, and It has become possible to provide a method for producing printed matter using the ink set.

  Further, according to another embodiment of the present invention, it has become possible to provide a printed matter having a poorly-absorbable substrate and having high color reproducibility and high-quality images.

  Hereinafter, the present invention will be described with reference to preferred embodiments. However, the embodiment described below shows an example of the embodiment of the present invention, and does not limit the scope of the present invention.

  In an embodiment of the present invention, two or more pigments containing an azo pigment and a diol-based solvent having a specific structure are included, and the amount of the cyclic amide-based solvent is defined as a certain amount or less while defining the amount thereof. I have. As a result, a high-quality image having high color developability, high sharpness, and high color reproducibility can be obtained without white spots, regardless of the base material, as well as storage stability, ejection stability, and drying property. And an excellent magenta ink for inkjet (hereinafter, also simply referred to as “ink”).

  As described in the section of the prior art, aqueous inks generally have a very high surface tension of water contained as a main component. Therefore, when an aqueous ink is printed on a substrate using an ink jet head, the ink penetrates into the substrate. Poor drying and / or white spots occur due to poor force and poor wetting spread. In particular, in the case of a poorly absorbable substrate, ink droplets that have landed adjacently coalesce before being sufficiently wetted and spread, which may cause color mixing bleeding and / or shading unevenness. Therefore, in order to obtain a printed matter having excellent print quality and drying properties, it is very important to improve the ink penetrating power and wet spreadability. Generally, an organic solvent and / or a surfactant is used in combination in order to improve the penetrating power and wet spreadability of the ink. In this case, the higher the hydrophobicity of the organic solvent used, the greater the effect of improving the penetrating power and wet spreadability.

  On the other hand, azo pigments are pigments having high coloring properties and excellent clarity, but have poor stability against organic solvents and surfactants, especially highly hydrophobic organic solvents. Therefore, when an organic solvent and / or a surfactant is used for the purpose of improving wet spreadability, the azo pigment is dissolved in these solvents, or the dispersion state of the azo pigment is destroyed by the surfactant. As a result, there is a possibility that the storage stability of the ink and the color development and clarity of the printed matter may be deteriorated. In addition, when the ink is kept in the ink jet head for a long period of time, the azo pigment dissolved in the organic solvent precipitates in the process of concentrating the ink, causing nozzle clogging and the like, leading to non-ejection. Was.

  As described above, conventionally, inks using azo pigments have a problem that it is difficult to achieve both storage stability, ejection stability, color development and clarity of an image, and excellent print image quality and drying property. Was. The inventors of the present invention have conducted intensive studies on this problem, and as a result, have included two or more types of pigments including an azo pigment and a diol-based solvent having a specific structure, defined the amount of the diol-based solvent, and included a cyclic amide-based solvent It has been found that the above-mentioned problems can be solved by setting the blending amount of the compound to a certain amount or less. Although it is inferred, the above configuration provides an image with no white spots, high color developability, high clarity, and high color reproducibility, as well as excellent storage stability, ejection stability, and drying property. The following are conceivable reasons for obtaining magenta ink.

  First, in an embodiment of the present invention, two or more pigments including an azo pigment and a diol-based solvent represented by the formula (1), wherein n is 1 and / or 2 (A-1) And the amount of the diol solvent (A-1) is 5 to 250 times the molar amount of the azo pigment. By using two or more types of pigments including an azo pigment, a spectral reflectance, which will be described later, is adjusted while taking advantage of the color developing properties and sharpness of the azo pigment, and a printed material having excellent color reproducibility is obtained. The “diol-based solvent (A-1) in which n is 1 and / or 2” refers to “the diol-based solvent in which n is 1 in the formula (1)” and / or “the diol-based solvent in which n is 2 in the formula (1). A diol-based solvent ”.

  The diol-based solvent (A-1) has a small molecular size and a large number of oxygen atoms in the molecular structure. Therefore, the diol-based solvent (A-1) is strongly bonded to an amide bond and a hydroxyl group present in the azo pigment molecule by a hydrogen bond, and is close to each other. It is thought to exist. Thus, it is considered that the azo pigment molecules are protected by the surrounding diol-based solvent (A-1), thereby preventing the dissolution and the dispersion state from being destroyed. As a result, even when used in combination with a highly hydrophobic organic solvent and / or a surfactant, as described above, the storage stability is deteriorated due to the dissolution and destruction of the dispersed state of the azo pigment, and the printed matter is deteriorated. It is considered that the deterioration of the coloring property and the sharpness and the non-discharge (deterioration of the discharge stability) are suppressed. Further, the diol-based solvent (A-1) molecule is linked to another diol-based solvent (A-1) molecule and other materials present in the ink by an interaction based on an intermolecular force. As a result, it is considered that the viscoelasticity of the ink becomes favorable, and the ejection stability at the time of high-speed printing can be further improved. The molar amount of the diol-based solvent (A-1) specified in the embodiment of the present invention is an amount sufficient to protect the azo pigment molecules and form an interaction with other materials. I have.

  On the other hand, among the diol solvents represented by the formula (1), the diol solvent (A-2) in which n is 3 and / or 4 is also considered to form a hydrogen bond with the azo pigment molecule. However, since the diol-based solvent (A-2) has a larger molecular size than the diol-based solvent (A-1), the diol-based solvent (A-2) has a weaker bond with the azo pigment molecule than the diol-based solvent (A-1). It is believed that the protection of the pigment molecules is insufficient. Therefore, in the embodiment of the present invention, the content of the diol-based solvent (A-2) is limited to 0.1 times or less of the content of the diol-based solvent (A-1), so that the effect of protecting the pigment is reduced. It is suitably expressed. The “diol-based solvent (A-2) in which n is 3 and / or 4” refers to ““ the diol-based solvent in which n is 3 in the formula (1) ”and / or“ the diol-based solvent in which n is 4 in the formula (1). A diol-based solvent ”.

  Further, since the cyclic amide solvent generally has a very high solubility, it is difficult to suppress the dissolution of the azo pigment even if the azo pigment is protected by the diol solvent (A-1). Therefore, in the embodiment of the present invention, the content of the cyclic amide-based solvent is also limited to 4.5% by mass or less based on the total amount of the ink, so that the insufficient protective effect is suppressed.

  As described above, in order to obtain an ink that satisfies the effects described above at the same time, an ink having the configuration of the embodiment of the present invention is preferable.

  Subsequently, each component contained in the ink of the embodiment of the present invention will be described below.

<Pigment>
<Azo pigment>
The magenta ink for inkjet according to the embodiment of the present invention contains two or more kinds of pigments, and one or more of them is an azo pigment. A printed matter having excellent clarity and gloss can be obtained, and the ejection stability, color development, and clarity can be improved by making the blend balance with the diol-based solvent (A-1) suitable. Therefore, the content of the azo pigment in the ink of the embodiment of the present invention is in the range of 0.5 to 8% by mass in the total amount of the ink and in the range of 35 to 100% by mass in the total amount of the pigment. The content of the azo pigment is preferably in the range of 1 to 8% by mass, more preferably 1.5 to 6.5% by mass, based on the total amount of the ink. In addition, the content of the azo pigment in the total amount of the pigment is preferably in the range of 50 to 100% by mass, and more preferably 65 to 100, from the viewpoint that an ink having particularly excellent storage stability, color development, and sharpness is obtained. It is more preferably in the range of mass%, particularly preferably in the range of 80 to 100 mass%.

  Further, the magenta ink for inkjet according to the embodiment of the present invention keeps the spectral reflectance of the ink-coated product described later in a suitable range, and obtains a printed matter having excellent ejection stability, and excellent coloring, clarity, and color reproducibility. Therefore, two or more azo pigments may be included as the azo pigment. Azo pigments that can be used in embodiments of the present invention include, but are not limited to, naphthol AS pigments, azo lake pigments, other monoazo pigments, disazo pigments, and the like.

  In the embodiment of the present invention, C.I. I. Pigment Red 31, 146, 147, 150, 170, 266, and 269 are preferably used. All of these pigments are also known as naphthol AS pigments. The naphthol AS pigment has good stability to an organic solvent compared to other azo pigments, has an ether bond and an amino group in the structure, and has a strong interaction with a diol solvent (A-1). It is conceivable that the effects of the embodiment of the present invention can be particularly suitably exerted. In addition, regardless of the type and amount of a material such as a water-soluble organic solvent and / or a surfactant to be used in combination, it is possible to make the ink excellent in ejection stability, color development and sharpness of an image. It is. Among the pigments exemplified above, azo pigments are at least C.I.C. because they exhibit sharpness of images and particularly high color reproducibility when used as an ink set. I. Pigment Red 146, 150, 170, and 266 are more preferable, and have a strong interaction with the diol-based solvent (A-1), storage stability of the ink, and coloring of the printed matter. At least C.I., from the viewpoint of excellent properties, sharpness, and color reproducibility. I. Pigment Red 150 is particularly preferred.

  The naphthol AS pigment is, for example, C.I. I. Taking Pigment Red 150 as an example, it is obtained by a coupling reaction between 3-amino-4-methoxybenzanilide and 3-hydroxy-2-naphthamide. Commercially available C.I. I. It is known that these materials partially remain in Pigment Red 150 (see Patent Document 5). Since these raw materials also contain an amino group and a hydroxyl group, it is considered that the interaction with the diol solvent (A-1) described above occurs. If the amount of the raw material contained as these impurities is large, C.I. I. Since the amount of the diol-based solvent (A-1) that interacts with Pigment Red 150 is reduced and the protection of the pigment may be insufficient, the effects of the embodiment of the present invention are sufficiently exhibited. Therefore, it is preferable to reduce the amount of these impurities. C. above. I. In the case of Pigment Red 150, the content of 3-amino-4-methoxybenzanilide and 3-hydroxy-2-naphthamide is preferably 8,000 ppm or less, more preferably, based on the total amount of the ink. Are respectively 6,000 ppm or less, more preferably 4,000 ppm or less, and particularly preferably 3,000 ppm or less. The content of the impurities can be measured by, for example, an HPLC method (high-performance liquid chromatography method).

In the embodiment of the present invention, it is also preferable to use an azo lake pigment as the azo pigment. In the present specification, the term "azo lake pigment" refers to a polyvalent compound having a high insolubilizing effect, such as Ca ²⁺ , Ba ²⁺ , Sr ²⁺ , Mn ²⁺ , or Al ³⁺ , with respect to a water-soluble azo colorant. Represents a pigment to which metal ions have been imparted and made insoluble. Azo lake pigments have very high color developability and tinting strength, and even if the content in the ink is small, an image excellent in color developability, clearness, and color reproducibility when used as an ink set can be obtained. Further, since the amount of the pigment itself that can cause non-discharge by dissolution and precipitation can be suppressed, the discharge stability can be improved.

  In the embodiment of the present invention, conventionally known azo lake pigments can be arbitrarily used. Among them, it is preferable to use a β-oxynaphthoic acid-based lake pigment. Examples of the β-oxynaphthoic acid-based lake pigment that can be used in the embodiment of the present invention include C.I. I. Pigment Red 48: 1, 48: 2, 48: 3, 52: 1, 52: 2, 57: 1, and 57: 2, and more preferably contains at least one selected from the group consisting of: From the viewpoint of color reproducibility when used as an ink set, at least C.I. I. Pigment Red 48: 3 is particularly preferred.

  In addition, in the embodiment of the present invention, from the viewpoints of storage stability, image clarity, and color reproducibility when used as an ink set, C.I. I. Pigment Red 1, 166, 185, and 242, at least one monoazo pigment and / or disazo pigment may be preferably used.

  As a preferred embodiment, from the viewpoint of obtaining a magenta ink for inkjet that has excellent storage stability, drying properties, and ejection stability, a naphthol AS pigment and a β-oxynaphthoic acid-based lake pigment may be used in combination. preferable. In that case, C.I. I. Pigment Red 146, 150, 170, and 266. I. Pigment Red 146 and Pigment Red 150, and more preferably C.I. from the viewpoints of storage stability of the ink and color development, clarity, and color reproducibility of the printed matter. I. Pigment Red 150 is particularly preferred. As a β-oxynaphthoic acid-based lake pigment used in combination with a naphthol AS pigment, C.I. I. Pigment Red 48: 1 and / or 48: 3 are preferred, and from the viewpoint of image clarity and color reproducibility when used as an ink set, at least C.I. I. Pigment Red 48: 3 is particularly preferred.

  When a naphthol AS pigment and a β-oxynaphthoic acid-based lake pigment are used in combination, the content of the β-oxynaphthoic acid-based lake pigment is based on the total amount of the naphthol AS pigment and the β-oxynaphthoic acid-based lake pigment. It is preferably from 50 to 99% by mass, more preferably from 70 to 97% by mass, and particularly preferably from 90 to 95% by mass. Although the details are unknown, an ink having excellent storage stability, ejection stability, and drying property can be obtained by using the above content.

  In the embodiments of the present invention, the expression that the ink contains “two or more types of pigments” means that the ink contains “two or more types of pigments having different chemical structures”. As for the solid solution pigment, since the solid solution pigment itself includes "two or more types of pigments having different chemical structures", for example, an ink containing one type of solid solution pigment is an ink containing "two or more types of pigments". I can say. The phrase "two or more pigments contain an azo pigment" means that "at least one selected from two or more pigments is an azo pigment". For example, all of the “two or more types of pigments” may be azo pigments, or only one of the “two or more types of pigments” may be an azo pigment, and the remaining one or more types may be other than the azo pigment. The pigment may be a pigment, or one or more of the “two or more types of pigments” may be an azo pigment, and only the other one may be a pigment other than the azo pigment.

<Other pigments>
The magenta ink for inkjet according to the embodiment of the present invention has a spectral reflectance of an ink-coated product described below within a suitable range, and has high color development, high clarity, high color reproducibility, and light fastness with respect to the inkjet printed material. Pigments other than azo pigments (hereinafter also referred to as “other pigments”) may be used as the two or more pigments in order to impart properties such as water resistance and water resistance. Among them, other pigments such as C.I. can be obtained from the viewpoint that a printed matter excellent in light resistance and water resistance can be obtained and the ejection stability of the ink used in combination is also excellent. I. It is preferable to select a quinacridone pigment such as CI Pigment Red 122, 202, 209, and 282, and Pigment Violet 19, and / or a solid solution pigment containing the quinacridone pigment. Among the quinacridone pigments exemplified above, the two or more pigments are at least C.I. in terms of excellent clarity of printed matter using an ink used in combination with an azo pigment and excellent color reproducibility when used as an ink set. I. Pigment Red 122 is particularly preferred.

In the embodiment of the present invention, when an azo pigment is used in combination with another pigment, the spectral reflectance in the wavelength range of 480 to 580 nm, which will be described later, is set to 10% or less, and the clarity and color reproducibility of the printed matter, and the discharge From the viewpoint of obtaining an ink having excellent stability, azo pigments used in combination with other pigments include C.I. I. Pigment Red 146, 150, 170, 266, 48: 1, and 48: 3 are preferable, and C.I. I. Pigment Red 150 and / or 48: 3 are particularly preferred.
When the azo pigment contains a naphthol AS pigment as the azo pigment, the content of the azo pigment is preferably more than 50% by mass and 99% by mass or less, more preferably 55 to 98% by mass. The content is more preferably 60 to 97% by mass, and particularly preferably 70 to 95% by mass.
On the other hand, when the azo pigment does not contain a naphthol AS pigment but contains a β-oxynaphthoic acid-based lake pigment, the content of the azo pigment is preferably from 35 to 55% by mass, and more preferably from 35 to 50% by mass based on the total amount of the pigment. More preferably, it is mass%.
In addition, as the azo pigment and the other pigment, two or more pigments may be used.

<Water-soluble organic solvent (A)>
<Diol-based solvent (A-1)>
The magenta ink for inkjet according to an embodiment of the present invention includes, as a water-soluble organic solvent (A), a diol-based solvent (A) in which n is 1 and / or 2 among diol-based solvents represented by Formula (1). -1) is contained in an amount of 5 to 250 times the molar amount of the azo pigment.

  As described above, the diol-based solvent (A-1) binds to the azo pigment by hydrogen bonding and prevents its dissolution, thereby preserving the storage stability, the coloring property of printed matter, clearness and color reproducibility, and the ejection stability. It is considered that the improvement of From the viewpoint of sufficiently protecting the azo pigment molecules and making the amount sufficient to form an interaction with other materials, the molar amount of the diol solvent (A-1) is determined by the molar amount of the azo pigment. The amount is preferably from 8 to 200 times, particularly preferably from 10 to 160 times.

  Specific examples of the diol solvent (A-1) in the embodiment of the present invention include ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol. Among these, it is preferable to contain ethylene glycol and / or propylene glycol from the viewpoint that the molecular size is small and the azo molecules can be suitably protected, and that the boiling point at 1 atm is low and the drying property of the ink can be improved. It is particularly preferable to include at least propylene glycol from the viewpoint of low surface tension and prevention of white spots on printed matter. In the embodiment of the present invention, as the diol-based solvent (A-1), the above solvent may be used alone, or two or more kinds may be used in combination. From the viewpoint of improving the storage stability and drying property of the ink, it is preferable that 50% by mass or more of the total amount of the diol-based solvent (A-1) is ethylene glycol and / or propylene glycol.

  In the embodiment of the present invention, the content of the diol-based solvent (A-1) is from the viewpoint that the storage stability and the ejection stability of the ink can be improved while improving the color developability and color reproducibility of the printed matter. The total amount of the ink is preferably 2 to 40% by mass, more preferably 5 to 37% by mass, and particularly preferably 8 to 35% by mass. As described above, the content of the diol-based solvent (A-1) is determined in consideration of the content of the azo pigment.

<Diol-based solvent (A-2)>
In the magenta ink for inkjet according to the embodiment of the present invention, as the water-soluble organic solvent (A), among the diol solvents represented by the formula (1), the diol solvent (A- 2) may be contained, but when it is contained, the content is 0.1 times or less the molar amount of the diol-based solvent (A-1). This is to prevent the protection of the azo pigment from being weakened by the diol-based solvent (A-1). As a result, from the viewpoint of obtaining an ink having excellent storage stability and discharge stability, and excellent color development and clarity of a printed matter, the molar amount of the diol-based solvent (A-2) is determined based on the diol-based solvent (A- The content is preferably not more than 0.05 times, more preferably not more than 0.02 times, even more preferably not more than 0.01 times the molar amount of 1).

  In the embodiment of the present invention, it is preferable that the diol-based solvent (A-2) is not substantially contained. In this specification, “substantially not contained” means that the material is not intentionally added, and does not exclude a trace amount of impurities and / or by-products. Specifically, it means that the material is 1% by mass, preferably 0.5% by mass or less, more preferably 0.2% by mass or less in the total amount of the ink. And particularly preferably 0.1% by mass or less.

  Specific examples of the diol solvent (A-2) in the embodiment of the present invention include triethylene glycol, tetraethylene glycol, tripropylene glycol, and tetrapropylene glycol. When the diol-based solvent (A-2) is used in the ink of the embodiment of the present invention, among the above, it is preferable to contain triethylene glycol and / or tripropylene glycol because of its low boiling point. In the embodiment of the present invention, when the diol-based solvent (A-2) is used, the above-mentioned solvent may be used alone, or two or more kinds may be used in combination.

<Cyclic amide solvent>
As described above, the magenta ink for inkjet according to the embodiment of the present invention substantially does not contain a cyclic amide-based solvent from the viewpoint of suppressing dissolution of the azo pigment and suitably exhibiting the effects of the embodiment of the present invention. If included, the content is set to 4.5% by mass or less based on the total amount of the ink jet magenta ink. In addition, from the above viewpoint, the content of the azo pigment is preferably 2.0% by mass or less in the total amount of the ink, and particularly preferably substantially not contained.

  Examples of cyclic amide solvents include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-vinyl-2-pyrrolidone, ε-caprolactam, N-methyl-ε-caprolactam, and N-ethyl-ε-caprolactam. , N-vinyl-ε-caprolactam and the like. When a cyclic amide-based solvent is used for the ink according to the embodiment of the present invention, from the viewpoint of the effect on the boiling point of the solvent, safety, and storage stability of the ink, 2-pyrrolidone and N-methyl It preferably contains one or more selected from pyrrolidone and ε-caprolactam. In the embodiment of the present invention, when a cyclic amide solvent is used, the above solvent may be used alone, or two or more solvents may be used in combination.

  In the embodiment of the present invention, the “cyclic amide-based solvent” is a compound having at least one cyclic structure and having at least one amide bond in the at least one cyclic structure, at 25 ° C. Refers to a compound that is a liquid.

<Other water-soluble organic solvents>
In the ink of the embodiment of the present invention, a water-soluble organic solvent other than the above-mentioned water-soluble organic solvent (A-1) can be used as long as the quality is not impaired. In the embodiments of the present invention, the “solvent” refers to a solvent that is liquid at 25 ° C. Other than those listed above, examples of the water-soluble organic solvent that can be used in the ink of the embodiment of the present invention include:
Monohydric alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 3-methoxy-1-butanol, 3-methyl-3-methoxybutanol;
1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5- Dihydric alcohols (diols) such as pentanediol, 3-methyl-1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol;
Polyhydric alcohols such as glycerin, diglycerin, butanetriol and hexanetriol;
Ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol isopropyl ether, diethylene glycol monobutyl ether, diethylene glycol isobutyl ether, diethylene glycol monopentyl ether, diethylene glycol mono Hexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol Lenglycol monoethyl ether, tetraethylene glycol monopropyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol Alkylene glycol monoalkyl ethers such as propylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and tripropylene glycol monoethyl ether;
Diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol methyl ethyl ether, diethylene glycol butyl Alkylene glycol dialkyl ethers such as methyl ether, triethylene glycol butyl methyl ether, and tetraethylene glycol butyl methyl ether;
And the like, but are not limited thereto. When other water-soluble organic solvents are used, the above-mentioned solvents may be used alone or in combination of two or more.

  In the embodiment of the present invention, it is preferable to use another water-soluble organic solvent having a static surface tension at 25 ° C. of 22 to 32 mN / m. In the embodiments of the present invention, the term “static surface tension of the ink” refers to a surface tension measured by a Wilhelmy method in an environment of 25 ° C. The static surface tension of the other water-soluble organic solvent used in the ink according to the embodiment of the invention is more preferably from 23 to 32 mN / m, and particularly preferably from 24 to 30 mN / m.

Further, in the embodiment of the present invention, when using another water-soluble organic solvent, it is preferable to contain at least one or more compounds having a boiling point of 120 to 250 ° C under 1 atm. It is more preferable to contain a certain compound, and it is particularly preferable to contain a compound having a temperature of 180 to 240 ° C. By setting the boiling point of the other water-soluble organic solvent to 120 ° C. or higher, drying on the inkjet head can be suppressed, and the ejection stability can be improved. When the temperature is 250 ° C. or lower, the residue after the drying step after printing can be prevented, and the color developability and sharpness of the printed matter can be improved. Among the compounds having a boiling point, from the viewpoint of compatibility with the azo pigment and the diol-based solvent (A-1), the total number of hydroxyl groups and / or ethylene oxide groups present in one molecule is 2 or more. Is preferably selected.
As described above, in the embodiment of the present invention, another water-soluble organic solvent is used from the viewpoint that it is preferably compatible with the azo pigment and the diol-based solvent (A-1) and does not inhibit the expression of the effects of the embodiment of the present invention. In this case, the other water-soluble organic solvent has a boiling point of 120 to 250 ° C. under one atmosphere, and the total number of hydroxyl groups and / or ethylene oxide groups in one molecule is two or more. It is particularly preferred to include certain dihydric alcohols (diols) and / or alkylene glycol monoalkyl ethers.

  As described above, the other water-soluble organic solvents in the embodiment of the present invention can be used within a range that does not impair the quality of the embodiment of the present invention. Specifically, the content thereof is 5% in the total amount of the magenta ink for inkjet. It is preferably from 50 to 50% by mass, more preferably from 10 to 45% by mass, and still more preferably from 15 to 40% by mass. The content is particularly preferably 20 to 35% by mass, and when the content is in the above range, the storage stability of the ink is also improved.

<Boiling point of water-soluble organic solvent>
The magenta ink for inkjet which is an embodiment of the present invention substantially does not contain or contains a water-soluble organic solvent having a boiling point of not less than 250 ° C. at 1 atm, the content thereof is based on the total amount of the magenta ink. It is preferably at most 9.5% by mass. By controlling the amount of the organic solvent within the above range, even when printing on a poorly absorbable substrate, the printing quality and drying properties are excellent, and the blocking (when the printed matter is stacked or wound up, the printing (A phenomenon that the back surface of the material is stained with ink) can be obtained. Further, from the viewpoint of more suitably exhibiting the above effects, the content of the water-soluble organic solvent having a boiling point of less than 250 ° C. at 1 atm is set to 6.5% by mass or less based on the total amount of the magenta ink (substantially). More preferably, it is not more than 3.5 mass% (it may not be substantially contained), more preferably, it is not more than 3.5 mass%, and it is more preferably 1.5 mass% or less (even if it is not substantially contained). Good) is particularly preferred, and it is extremely preferred that they are not substantially contained. In calculating the content of the water-soluble organic solvent having a boiling point of 250 ° C. or more at 1 atm, the diol solvent (A-1), the diol solvent (A-2), and the cyclic amide solvent are also considered. It shall be put in. That is, “the content of the water-soluble organic solvent having a boiling point of 1 ° C. or more at 250 ° C. or more” is all of the “water-soluble organic solvents having a boiling point of 1 ° C. or more of 250 ° C. or more” contained in the ink. It is the total content of the solvent.

  For the same reason as above, it is preferable that the magenta ink for inkjet of the embodiment of the present invention does not substantially contain a water-soluble organic solvent having a boiling point of 290 ° C. or more at 1 atm. Examples of the water-soluble organic solvent having a boiling point of 290 ° C. or more at 1 atm include glycerin, diglycerin, butanetriol, and hexanetriol.

  Furthermore, the weight-average boiling point under 1 atm of the water-soluble organic solvent contained in the magenta ink for inkjet of the embodiment of the present invention is preferably 150 to 245 ° C, more preferably 170 to 235 ° C. The temperature is more preferably 180 to 220 ° C, particularly preferably 185 to 210 ° C. By keeping the weighted boiling point average value of the water-soluble organic solvent within the above range, even when printing on a poorly absorbent substrate, it is possible to obtain a printed matter having excellent print quality and drying properties, and also excellent discharge stability. It will be. In calculating the weighted boiling point average, the diol solvent (A-1), the diol solvent (A-2), and the cyclic amide solvent are also taken into consideration. That is, the “weighted boiling point average value of the water-soluble organic solvent at 1 atm” is the weighted boiling point average value of all solvents corresponding to the “water-soluble organic solvent” contained in the ink. The weighted boiling point average value at 1 atm is obtained by adding the multiplication value of the boiling point at 1 atm and the mass ratio to the total water-soluble organic solvent calculated for each water-soluble organic solvent. Value.

<HLB value of water-soluble organic solvent>
As the water-soluble organic solvent contained in the magenta ink for inkjet according to the embodiment of the present invention, those having an HLB value of 7 to 11 calculated by a method described later can be suitably used. In addition, it is particularly preferable to use one having an HLB value of 7.5 to 10. The HLB (Hydrophile-Lipophile Balance) value is one of parameters indicating the hydrophilicity and / or hydrophobicity of a material. The smaller the HLB value, the higher the hydrophobicity of the material, and the higher the HLB value, the higher the hydrophilicity of the material. Represents A water-soluble organic solvent having an HLB value of 7 to 11 has a suitable balance between hydrophilicity and hydrophobicity, and can suppress dissolution of the azo pigment in the water-soluble organic solvent and destruction of the dispersed state of the azo pigment, As a result, a magenta ink excellent in storage stability and ejection stability can be obtained. In addition, as shown in the table of Examples described later, all of the diol solvents (A-1) which are essential components in the magenta ink for inkjet according to the embodiment of the present invention have an HLB value of 7 to 11.

<Surfactant>
The magenta ink for inkjet according to the embodiment of the present invention contains a surfactant. By containing a surfactant, not only can the wetting and spreading property on the base material be controlled to prevent white spots on the printed matter, but also the meniscus in the inkjet head can be suitably controlled and the ejection stability can be improved. .

  In particular, in the embodiment of the present invention, the HLB value of the surfactant can be ensured in addition to ensuring compatibility with the diol solvent (A-1) and protecting the azo pigment together with the diol solvent (A-1). Is preferably 7 to 20. In particular, surfactants that do not contribute to the protection of the azo pigments are uniformly oriented at the interface between the ink and the substrate, and improve wettability and spreadability on various substrates including a poorly absorbable substrate. The HLB value of the surfactant is more preferably from 9 to 19, and particularly preferably from 12 to 18, from the viewpoint that a printed matter having excellent print quality is obtained.

  On the other hand, when an azo pigment and another pigment are used in combination as the two or more kinds of pigments, white spots on the printed matter are prevented without deteriorating the storage stability of the ink, and the ejection stability is also improved. From the viewpoint that an excellent magenta ink can be obtained, it is also preferable to use a surfactant having an HLB value of 2 to 7, and particularly to use a surfactant having an HLB value of 2.5 to 6. It is suitable.

  Note that there are various methods for calculating the HLB value, such as the Griffin method, the Davis method, and the Kawakami method, and various actual measurement methods are known. In the embodiment of the present invention, the above-described water-soluble organic solvent, When the structure of the compound is clearly known, such as an acetylene-based surfactant and a glycol ether-based surfactant described below, the HLB value is calculated using the Griffin method. The Griffin method is a method of obtaining an HLB value as in the following formula (I) using the molecular structure and molecular weight of a target material.

Formula (I):

HLB value = 20 × (total molecular weight of hydrophilic portion) ÷ (molecular weight of material)

  On the other hand, when a compound having an unknown structure is contained, such as a siloxane-based surfactant, for example, see “Handbook of Surfactants” (edited by Nishiichiro et al., Sangyo Tosho Co., Ltd., 1960), p. The HLB value of the surfactant can be experimentally determined by the following method described in H.324. Specifically, after dissolving 0.5 g of the surfactant in 5 mL of ethanol, the obtained solution is stirred at 25 ° C. and titrated with a 2% by mass aqueous phenol solution. And Assuming that the amount of the phenol aqueous solution required up to the end point is A (mL), the HLB value can be calculated by the following formula (II).

Formula (II):

HLB value = 0.89 × A + 1.11

  Various surfactants such as acetylene-based, siloxane-based, fluorine-based, and glycol ether-based surfactants are known according to the intended use. In the embodiment of the present invention, any surfactant is used. Can be used alone or in combination.

  Among them, from the viewpoint of interaction with the diol-based solvent (A-1), it is preferable to use at least one selected from acetylene-based surfactants, siloxane-based surfactants, and glycol ether-based surfactants. It is more preferable to use at least an acetylene-based surfactant. In a preferred embodiment, it is also preferable to use an acetylene-based surfactant in combination with a siloxane-based surfactant and / or a glycol ether-based surfactant. By using both of them, the dynamic surface tension and the static surface tension of the ink can be suitably adjusted, and it is possible to achieve both image quality, drying property, and ejection stability of the printed matter.

  In the embodiment of the present invention, the surfactant preferably has an ethylene oxide and / or propylene oxide group from the viewpoint of miscibility with the diol solvent (A-1). For example, in the case of a siloxane-based surfactant, it is preferable to use a polyether-modified polydimethylsiloxane. Among the polyether-modified polydimethylsiloxanes, a polyether group has a polyether group at a side chain of a polydimethylsiloxane chain and / or at both ends. It is highly preferred to use one. Furthermore, from the viewpoint that the orientation speed at the interface between the ink and the base material is high, and particularly excellent print quality is obtained, it is most preferable to use a siloxane-based surfactant having a polyether group in the side chain of the polydimethylsiloxane chain. preferable.

  In the case of an acetylene-based surfactant, for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecine-5,8 -Diol, hexadec-8-yne-7,10-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, and 7,10-dimethylhexadeca-8-yne-7,10- Preferred are ethylene oxide adducts and / or propylene oxide adducts of compounds selected from diols. Note that one molecule may have both an ethylene oxide group and a propylene oxide group. In this case, the order of addition of the ethylene oxide group and the propylene oxide group does not matter, and the addition form may be block or random.

  Further, in the case of a glycol ether surfactant, a compound represented by the following formula (2) can be suitably used.

Equation (2):

RO- (AO) m-H

  In the above formula (2), R represents an optionally branched alkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, an alkylcarbonyl group having 8 to 22 carbon atoms, or 8 carbon atoms. ~ 22 alkenylcarbonyl groups. AO represents an ethylene oxide group or a propylene oxide group, and m represents an integer of 1 to 100. However, one molecule may have both an ethylene oxide group and a propylene oxide group. In that case, the order of addition of the ethylene oxide group and the propylene oxide group does not matter, and the addition form may be block or random.

  The content of the surfactant in the inkjet magenta ink of the embodiment of the present invention is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 4.5% by mass based on the total amount of the ink. %, More preferably 0.5 to 4.0% by mass, and particularly preferably 0.7 to 3.5% by mass.

<Pigment dispersion resin>
When the azo pigment is used in the embodiment of the present invention, it is preferable to use the azo pigment dispersed in the ink in order to maintain the storage stability of the ink for a long period of time and to secure the ejection stability after standby. Examples of the method for dispersing the pigment include a method in which the surface of the pigment is modified by an oxidation treatment or the like and the pigment is dispersed without a dispersant, or a method in which the pigment is dispersed using a surfactant and / or a resin as a dispersant. In order to obtain an ink having better storage stability and ejection stability, it is preferable to disperse the pigment using a pigment dispersion resin.

  The “pigment-dispersed resin” in the embodiment of the present invention includes (1) a water-soluble pigment-dispersed resin used by being adsorbed on a pigment surface, and (2) a pigment-dispersed resin (water-soluble resin) used for coating a pigment. , Or water-insoluble). The term “water-soluble resin” refers to a resin in which a 1% by mass aqueous solution of a target resin is transparent to the naked eye at 25 ° C.

  Examples of the pigment dispersion resin include a (meth) acrylic resin, a maleic acid resin, an α-olefin maleic resin, a urethane resin, and an ester resin. Among them, it is preferable to use a (meth) acrylic resin from the viewpoint that the configuration can be easily changed and / or adjusted so that the interaction between the azo pigment and the diol-based solvent (A-1) can be assisted. In addition, it strengthens the adsorption of the pigment and improves the dispersion stability of the pigment by stabilizing the pigment dispersion, thereby improving the ejection stability and the excellent color development on the poorly-absorbable base material. From the viewpoint of securing, it is preferable that among the acrylic resins, a (meth) acrylic resin containing a monomer containing an aromatic ring in the copolymer composition is included. In this specification, “(meth) acrylic resin” refers to a methacrylic monomer (for example, methacrylic acid, methyl methacrylate, butyl methacrylate, ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, benzyl methacrylate, methacrylic acid). At least one of phenoxyethyl acrylate, etc.) and acrylic monomers (eg, acrylic acid, methyl acrylate, butyl acrylate, ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, phenoxyethyl acrylate, etc.) It means a resin containing the above monomer as a component. The (meth) acrylic resin that can be used in the embodiment of the present invention may further include a styrene-based monomer (for example, styrene, methylstyrene, methoxystyrene, or the like) as a constituent monomer.

  Examples of the aromatic ring structure include a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, and an anisyl group. Among them, a phenyl group or a tolyl group is preferred from the viewpoint of the dispersion stability of the pigment.

  The weight average molecular weight of the pigment dispersion resin that can be used in the embodiment of the present invention is preferably 5,000 to 100,000. When the weight average molecular weight is 5,000 or more, dispersion stabilization can be sufficiently realized, and agglomeration of the azo pigment at the time of drying can be prevented. When the weight average molecular weight is 100,000 or less, an excessive increase in ink viscosity can be prevented even after water is volatilized. In particular, when the ink-jet printer is kept on standby for a long time, the ink viscosity increases when water evaporates near the ink-jet nozzle and the ink is concentrated, leading to problems such as non-ejection. By keeping the ink inside, the ink ejection stability can be improved. The weight average molecular weight of the pigment-dispersed resin is more preferably from 10,000 to 80,000, particularly preferably from 15,000 to 50,000, in order to secure ejection stability and obtain excellent print quality.

  The weight average molecular weight of the pigment dispersion resin in the present invention can be measured by a conventional method. As an example, using a TSKgel column (manufactured by Tosoh Corporation), a GPC equipped with an RI detector (manufactured by Tosoh Corporation, HLC-8120GPC) is used, and the weight average in terms of polystyrene measured using THF (tetrahydrofuran) as a developing solvent. Determined as molecular weight.

  Furthermore, the pigment dispersion resin of the embodiment of the present invention preferably contains a monomer having an alkyl chain having 8 to 30 carbon atoms in the copolymer composition. Improves the dispersion stability and secures the ejection stability from the inkjet head, and on the poorly absorbable base material, maintains the dispersion stability of the pigment during the drying process, and also maintains the color development and gloss by maintaining the pigment dispersion resin. From the viewpoint of expression, an alkyl chain having 10 to 28 carbon atoms is more preferable, and an alkyl chain having 12 to 24 carbon atoms is particularly preferable.

  The alkyl chain having 8 or more carbon atoms may be linear or branched, but is preferably a linear one. Examples of the alkyl chain include an octyl group (C8), an ethylhexyl group (C8), a decyl group (C10), a lauryl group (C12), a myristyl group (C14), a cetyl group (C16), a stearyl group (C18), and an aralkyl group (C20). ), A behenyl group (C22), a lignoseryl group (C24), a serotoyl group (C26), a montanyl group (C28), and a merissyl group (C30).

  The content of the monomer having an alkyl chain having 8 to 30 carbon atoms, which is contained in the pigment dispersion resin as a constituent component, is to lower the viscosity of the pigment dispersion and to reduce the abrasion resistance, drying property, and blocking resistance of the printed matter. It is preferably 5 to 60% by mass, more preferably 15 to 55% by mass, and particularly preferably 25 to 50% by mass from the viewpoint of achieving a balance between the properties, the color developing properties, and the glossiness.

  It is also preferred that the pigment dispersion resin contains an alkylene oxide group in addition to the aromatic ring structure. By introducing an alkylene oxide group, the hydrophilicity and hydrophobicity of the pigment-dispersed resin can be arbitrarily adjusted, and the storage stability of the aqueous ink can be improved. At the same time, the alkylene oxide group causes a hydrogen bond with the diol-based solvent (A) in the ink, so that the diol-based solvent (A) suitably exerts a protective effect on the azo pigment, leading to an improvement in the above properties. When a water-soluble pigment-dispersed resin is used as the pigment-dispersed resin, the ethylene oxide group is preferably selected as the alkylene oxide group, so that the above functions can be suitably exhibited. Similarly, when a water-insoluble pigment dispersion resin is used as the pigment dispersion resin, it is preferable to select a propylene oxide group as the alkylene oxide group.

  The content of the monomer having an alkylene oxide group, which is contained in the pigment dispersion resin as a component, is preferably 5 from the viewpoint of reducing the viscosity of the pigment dispersion, the storage stability of the ink, and the adhesion of the printed matter. It is preferably from 40 to 40% by mass, more preferably from 10 to 35% by mass, and particularly preferably from 15 to 30% by mass.

  When a water-soluble pigment dispersion resin is used as the pigment dispersion resin, the acid value of the pigment dispersion resin suitably used in the embodiment of the present invention is 30 to 400 mgKOH / g. When the acid value falls within the above range, the solubility of the pigment-dispersed resin in the ink can be ensured, and the viscosity of the ink can be suppressed to a suitable range. The acid value of the pigment dispersion resin is more preferably from 70 to 350 mgKOH / g, and still more preferably from 100 to 300 mgKOH / g.

  On the other hand, when a water-insoluble pigment-dispersed resin is used as the pigment-dispersed resin, its acid value is preferably from 0 to 100 mgKOH / g, more preferably from 5 to 90 mgKOH / g, even more preferably from 10 to 80 mgKOH / g. g. This is because by keeping the acid value within the above range, a printed material having excellent blocking resistance and abrasion resistance can be obtained.

  The acid value of the pigment-dispersed resin is the number of mg of potassium hydroxide (KOH) required for neutralizing the acid contained in 1 g of the pigment-dispersed resin. It is a value obtained by titration at. The measurement can be performed using, for example, "Automatic Potentiometric Titrator AT-610" manufactured by Kyoto Electronics Industry Co., Ltd.

  When a water-soluble pigment-dispersed resin is used as the pigment-dispersed resin, the acid groups in the resin are preferably neutralized with a base in order to increase the solubility in water. As the base, organic bases such as aqueous ammonia, dimethylaminoethanol, diethanolamine, and triethanolamine, and inorganic bases such as lithium hydroxide, sodium hydroxide, and potassium hydroxide can be used. When an organic base is used, the base is volatilized when the ink is dried, and the water resistance of the printed matter may be improved.

  The ratio of the pigment-dispersed resin to the pigment in the embodiment of the present invention is preferably 2 to 60% by mass. When the ratio of the pigment-dispersed resin to the pigment is 60% by mass or less, the viscosity of the ink can be suppressed low, and the ejection stability is improved. When the ratio of the pigment dispersion resin to the pigment is 2% by mass or more, the storage stability is improved. From the viewpoint of ensuring excellent storage stability and ejection stability, and obtaining a printed material having higher color developability, the ratio of the pigment-dispersed resin to the pigment is more preferably 4 to 55% by mass, and still more preferably. 5 to 50% by mass.

<Binder resin>
In the magenta ink for inkjet according to the embodiment of the present invention, a binder resin can be used even if it is on a poorly absorbable substrate, so as to make the ink excellent in drying property and resistance. In the embodiment of the present invention, the “binder resin” is used for bringing the printed matter into close contact with the hardly-absorbable base material and for imparting abrasion resistance and water resistance to the printed matter. Further, the binder resin may also have a function of stabilizing the dispersion state of the azo pigment in the ink. However, in the embodiment of the present invention, it is better that the pigment-dispersed resin and the binder resin have distinct functions. Therefore, in the embodiment of the present invention, it is preferable that two or more types of resins having different configurations are contained in the ink. Note that the surfactant described above does not correspond to “resin”.

  In the case where the target resin is a water-soluble resin, it is possible to discriminate which of the pigment-dispersed resin and the binder resin has the function based on the adsorption rate to the pigment. That is, a pigment dispersion containing a pigment, a resin, and an aqueous medium (a liquid containing at least water). The pigment concentration is 5% by mass, and the amount of water is 98% by mass or more in the total amount of the aqueous medium. In the prepared pigment dispersion, a resin having an adsorption rate of the resin to the pigment of 35% by mass or more is referred to as a pigment-dispersed resin, and a resin having a ratio of less than 35% by mass is referred to as a binder resin. The amount of the water is preferably 100% by mass based on the total amount of the aqueous medium.

  For example, magenta ink is C.I. I. Pigment Red 150 and C.I. I. When Pigment Red 48: 3 is contained in a mass ratio of 1: 1, the pigment dispersion used for the measurement of the adsorption rate is the same as the production example of the magenta pigment dispersion 1 described in Examples described later. After preparing a high-concentration pigment dispersion having a pigment concentration (total amount) of 20% by mass, the pigment dispersion is diluted with water until the pigment concentration becomes 5% by mass. Further, the adsorption rate is determined, for example, by performing an ultracentrifugation treatment (for example, at 30,000 rpm for 4 hours) on the pigment dispersion, measuring the amount of resin contained in the supernatant, and obtaining the following formula (3). ) Can be calculated.

Equation (3):

Adsorption rate (%) = (WR1-WR2) × 100 / WR1

  However, in the above formula (3), WR1 represents the amount of resin contained in the pigment dispersion before ultracentrifugation, and WR2 represents the amount of resin contained in the supernatant.

  For the measurement of the adsorption rate, the same pigment as the pigment actually contained in the magenta ink is used as the pigment.

  As the binder resin in the ink, a water-soluble resin and resin fine particles are known, and both can be suitably used in the embodiment of the present invention. Generally, resin fine particles have a higher molecular weight than a water-soluble resin, and can provide high resistance. On the other hand, the water-soluble resin is easily redissolved even after the film is formed once, and can prevent the deterioration of the ejection stability. In the embodiment of the present invention, the water-soluble resin and the resin fine particles are distinguished by having a specific particle diameter in water. Specifically, using a particle size distribution analyzer (for example, Microtrac UPA EX-150 manufactured by Microtrac Bell Inc.), the cumulative 50% diameter value (median diameter, median diameter, (Hereinafter referred to as "D50") is 30 nm or more as "resin fine particles", and those having a particle diameter of less than 30 nm or in which D50 cannot be measured are referred to as "water-soluble resins". D50 is a measured value in a 25 ° C. environment, and when measuring with the above-mentioned apparatus, the sample is diluted with water as needed to adjust to a measurable concentration.

  Examples of the binder resin used in the embodiment of the present invention include (meth) acrylic resin, urethane resin, styrene butadiene resin, vinyl chloride resin, polyolefin resin, and the like, but are not limited thereto. It is preferable to use (meth) acrylic resin from the viewpoint of ensuring the stability of ejection from the inkjet nozzle.

  The weight average molecular weight of the binder resin used in the embodiment of the present invention is from 3,000 to ensure excellent ejection stability from an inkjet nozzle and obtain excellent resistance even on a poorly absorbent substrate. It is preferably 300,000, more preferably 5,000 to 200,000, and particularly preferably 10,000 to 100,000. When the weight average molecular weight is within the above range, even when water in the ink volatilizes at the end face of the ink jet nozzle, it is possible to prevent the ink from increasing in viscosity and from non-ejection. The weight average molecular weight of the binder resin in the present invention can be measured in the same manner as in the case of the pigment dispersion resin.

  In the embodiment of the present invention, it is possible to further improve the resistance such as abrasion resistance and chemical resistance by increasing the glass transition temperature (Tg) of the binder resin. The glass transition temperature (Tg) of the binder resin is preferably in the range of 40 to 120C, more preferably in the range of 50 to 110C. When the glass transition temperature (Tg) is 40 ° C. or higher, better resistance is easily obtained, and it is preferable in practical use from the viewpoint of suppressing peeling of prints from printed matter. Further, when the glass transition temperature (Tg) is 120 ° C. or lower, the hardness of the printed matter is easily maintained in an appropriate range, and it is preferable from the viewpoint of suppressing cracks and cracks on the printed surface when the printed matter is bent.

  The inventors of the present invention have studied that, by using an azo lake pigment as an azo pigment and using a binder resin having a glass transition temperature (Tg) of 40 to 120 ° C., storage stability, discharge stability, and printed matter can be improved. It was found that a magenta ink excellent in color development and sharpness was obtained. As a hypothesis, generally, a resin having a high glass transition temperature (Tg) has a highly polar substituent, an aromatic ring structure, and / or a functional group that forms a hydrogen bond in a resin molecular structure. On the other hand, an azo lake pigment is a combination of a water-soluble azo colorant and a polyvalent metal ion, and it is considered that the polarity of pigment molecules is larger than other pigments. As a result, the azo lake pigment forms a bond based on the intermolecular force and the like with the resin having the above-mentioned glass transition temperature (Tg), thereby deteriorating the storage stability, the ejection stability, and the coloring and sharpness of the printed matter. Is considered to be suppressed.

  The above glass transition temperature is a value obtained by using a DSC (differential scanning calorimeter), and can be measured, for example, as follows. About 2 mg of the sample in which the binder resin has been dried is weighed on an aluminum pan, the test container containing the sample is set in the DSC measurement holder, and the endothermic peak of the chart obtained under the temperature rising condition of 5 ° C./min is read. The peak temperature at this time is defined as the glass transition temperature in this specification.

  The acid value of the binder resin that can be used in the embodiment of the present invention is preferably 1 to 100 mgKOH / g, and more preferably 5 to 80 mgKOH, from the viewpoint of improving resistance such as abrasion resistance, water resistance, and chemical resistance. / G, more preferably 10 to 60 mgKOH / g. In addition, the acid value of the binder resin in the embodiment of the present invention can be measured in the same manner as in the case of the pigment-dispersed resin.

  The content of the binder resin in the ink composition is preferably in the range of 1 to 20% by mass, more preferably 3 to 15% by mass of the total mass of the ink in terms of nonvolatile components.

<Water>
As the water contained in the magenta ink for inkjet according to the embodiment of the present invention, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

  The content of water that can be used in the embodiment of the present invention is in the range of 20 to 90% by mass based on the total mass of the ink.

<Other ingredients>
In the ink of the embodiment of the present invention, in addition to the above-described components, additives such as an antifoaming agent and a preservative may be appropriately added in order to obtain an ink having desired physical properties as needed. Can be. An example of the addition amount of these additives is preferably from 0.01% by mass to 10% by mass with respect to the total mass of the ink.

<Dynamic surface tension of ink>
The magenta ink for inkjet according to the embodiment of the present invention is calculated by a maximum bubble pressure method in order to quickly spread and spread at the moment of landing on a poorly absorbent substrate, and to provide excellent print quality without white spots and density unevenness. The dynamic surface tension of the ink at 10 milliseconds is preferably from 25 to 45 mN / m, and more preferably from 25 to 35 mN / m. Specifically, the dynamic surface tension at 25 ° C. was measured using a bubble pressure dynamic surface tensiometer BP100 (manufactured by Kruss) using the maximum bubble pressure method. Can be calculated.

<Ink particle size distribution>
In the magenta ink for inkjet of the embodiment of the present invention, in addition to storage stability and ejection stability, from the viewpoint of making the ink excellent in color development of printed matter, clarity, and color reproducibility, for example, a suitable material It is preferable to control the particle size distribution of the pigment contained in the ink by selection and control of the dispersion step described below. Specifically, D50 measured using a particle size distribution analyzer (Microtrack UPAEX-150 manufactured by Microtrac Bell Inc.) used for the particle size distribution measurement of the binder resin is preferably 30 to 300 nm, It is more preferably from 50 to 260 nm, particularly preferably from 70 to 220 nm. Further, the 90% cumulative diameter value on a volume basis is preferably 800 nm or less, more preferably 650 nm or less, and particularly preferably 500 nm or less. As described above, the ink according to the embodiment of the present invention includes two or more types of pigments. The particle size distribution is measured in a state where two or more types of pigments are included.

<Ink set>
The magenta ink for inkjet according to the embodiment of the present invention may be used in a single color, but may be used as an ink set in which a plurality of colors are combined according to the application. The combination is not particularly limited, but a full-color image can be obtained by using three colors of cyan, yellow, and magenta. Further, by adding the black ink, the black feeling can be improved, and the visibility of characters and the like can be improved. Furthermore, color reproducibility can be improved by adding a color such as orange or green. When printing on a printing substrate other than white, a clear image can be obtained by using white ink in combination.

  When a combination including cyan, yellow, and magenta is used as the inkjet ink set of the embodiment of the present invention, a suitable pigment type is selected from the viewpoint of excellent color reproducibility when printed on a poorly absorbent substrate. . Examples of cyan pigments include C.I. I. Pigment Blue 15: 3, 15: 4, and 15: 6. As the yellow pigment, C.I. I. Pigment Yellow 12, 13, 14, 74, 83, 120, 150, and 180 are preferred, and from the viewpoint of suppressing color mixture bleeding and obtaining high color reproducibility, C.I. I. Pigment Yellow 14, 74 and 180.

  In the embodiment of the present invention, it is preferable that the cyan ink and the yellow ink included in the inkjet ink set contain a diol-based solvent (A-1). In particular, when heat energy is applied collectively after printing all the inks included in the ink set, each ink comes into contact on the printing base material. At that time, if the cyan ink and the yellow ink contain the diol-based solvent (A-1), the dissolution of the azo pigment and the destruction of the dispersed state can be suppressed in the magenta ink that comes into contact with the cyan ink and the yellow ink. Thus, a printed matter having excellent coloring properties and sharpness can be obtained.

  In addition, from the viewpoint of obtaining a printed matter having particularly excellent color developing properties, sharpness, and color reproducibility, the diol-based solvent (A) contained in each of the cyan ink, yellow ink, and magenta ink included in the inkjet ink set is used. The molar content of -1) is preferably 5-250 times the molar content of the azo pigment in the magenta ink. Among them, from the viewpoint of obtaining a printed matter excellent in color developability and clarity regardless of conditions, such as a printing substrate and a printing speed, contained in the inkjet ink set, a cyan ink, a yellow ink, and a magenta ink are included. The content of the diol-based solvent (A-1) is particularly preferably from 10 to 200 times the content of the azo pigment in the magenta ink.

Furthermore, regardless of the method of applying heat energy described below, from the viewpoint of obtaining a printed matter excellent in color developability, clarity, and color reproducibility, each of the inks (including at least the magenta ink) included in the inkjet ink set is used. In the ink in which each of the inks (including at least the magenta ink) that are brought into contact with each other in a wet state at the time of printing are mixed in equal amounts, the content of the diol-based solvent (A-1) with respect to the content of the azo pigment is calculated. The amount is preferably from 5 to 250 times, particularly preferably from 10 to 200 times.
When the ink set includes a black ink, the above molar content and double amount are calculated except for the black ink. For example, among the respective inks included in the ink set, the cyan ink, the yellow ink, and the magenta ink, which are the three primary colors, may be included in the above-described range, and the double amount calculated using the inks mixed in equal amounts may be included. preferable. Also, for example, since all the inks included in the ink set may come into contact with each other in a wet state on the substrate at the time of printing, all the inks included in the ink set except for the black ink are used in equal amounts. It is preferable that the double amount calculated using the inks mixed at a time is included in the above range. More preferably, the three primary colors cyan ink, yellow ink, and a double amount calculated using an ink obtained by mixing equal amounts by selecting the magenta ink, and excluding the black ink, excluding all the inks included in the ink set Both the double amount calculated using the ink mixed in equal amounts are included in the above range.

  In addition, when a combination including cyan, yellow, and magenta is used as an inkjet ink set, cyan ink has excellent wet-spreading properties on a poorly-absorbable substrate and can suppress the color mixture bleeding between droplets. It is preferable that the yellow ink contains at least one surfactant having an HLB value of 8 to 20 and is combined with the magenta ink of the embodiment of the present invention.

  Further, when using a combination including cyan, yellow, and magenta as an inkjet ink set, to improve wet spreadability upon impact on a poorly absorbent substrate and achieve excellent print image quality and color reproducibility, The dynamic surface tension at 10 milliseconds calculated by the maximum bubble pressure method is preferably 25 to 45 mN / m, more preferably 25 to 35 mN / m for each ink.

<Ink preparation method>
Examples of a method for preparing an ink containing the above components include the following methods, but embodiments of the present invention are not limited thereto.

<(1) Production of pigment dispersion>
When a water-soluble pigment-dispersed resin is used as the pigment-dispersed resin, the water-soluble pigment-dispersed resin, water and, if necessary, a water-soluble organic solvent such as a diol-based solvent (A-1) are mixed and stirred, and A pigment-dispersed resin mixture is prepared. After the pigment is added to the water-soluble pigment-dispersed resin mixture, mixed and stirred (premixed), a dispersion treatment is performed using a disperser. Thereafter, if necessary, centrifugation, filtration, and adjustment of the solid content concentration are performed to obtain a pigment dispersion.

  Further, when preparing a dispersion of a pigment coated with a water-insoluble pigment dispersion resin, in advance, the water-insoluble pigment dispersion resin was dissolved in an organic solvent such as methyl ethyl ketone, and the water-insoluble pigment dispersion resin was neutralized as necessary. Then, a water-insoluble pigment-dispersed resin solution is prepared. The pigment and water are added to the water-insoluble pigment dispersion resin solution, mixed and stirred (premixing), and then subjected to a dispersion treatment using a disperser. Thereafter, the organic solvent was distilled off by distillation under reduced pressure, and if necessary, centrifugation, filtration, and adjustment of the solid content concentration using water and / or a diol-based solvent (A-1) were performed. A pigment dispersion is obtained.

  The dispersing machine used for the dispersion treatment of the pigment may be any commonly used dispersing machine, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among these, a bead mill is preferably used, and specifically, it is commercially available under trade names such as a super mill, a sand grinder, an agitator mill, a Glen mill, a Dyno mill, a pearl mill, and a Kobol mill.

  Regardless of which pigment dispersing resin is used, it is effective to perform premixing before the dispersion treatment performed when preparing the pigment dispersion. Premixing may be performed by adding a pigment to an aqueous medium in which at least a pigment dispersion resin and water are mixed.

  The dispersing machine used for the dispersion treatment of the pigment may be any commonly used dispersing machine, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, a microfluidizer, and a nanomizer. Among them, a bead mill is preferably used, and specifically, it is commercially available under the trade names of super mill, sand grinder, agitator mill, Glen mill, Dyno mill, pearl mill and Kobol mill.

  In the premixing and dispersion treatment of the pigment, the pigment dispersant may be dissolved or dispersed only in water, or may be dissolved or dispersed in a mixed solvent of an organic solvent and water.

  As the pigment contained in the ink of the embodiment of the present invention, it is preferable to use a pigment having an optimum particle size distribution as described above. In order to obtain a pigment having a desired particle size distribution, the following method can be used. Reducing the size of the grinding media of the dispersing machine as described above; changing the material of the grinding media; increasing the filling ratio of the grinding media; changing the shape of the stirring member (agitator); Prolonging the treatment time; classifying with a filter and a centrifuge after dispersion treatment; and a combination of these methods. In order to keep the pigment in the embodiment of the present invention in the above-mentioned preferable particle size range, the size of the pulverizing media of the dispersing machine is preferably 0.1 to 3 mm in diameter. Glass, zircon, zirconia, or titania is preferably used as the material of the pulverizing media.

  In the production of the ink of the embodiment of the present invention, after producing a pigment dispersion for each pigment, the ink may be prepared by mixing, or a pigment dispersion containing two or more pigments, An ink may be prepared. However, when a water-soluble pigment-dispersed resin is used as the pigment-dispersed resin, a method of producing a pigment dispersion liquid containing two or more pigments is not known in detail, but from the viewpoint of obtaining an ink having excellent storage stability and coloring properties. It is preferably selected. On the other hand, when a water-insoluble pigment-dispersed resin is used as the pigment-dispersed resin, a method of producing a pigment dispersion liquid for each pigment is preferably selected from the viewpoint that the coloring properties and sharpness of each pigment can be sufficiently expressed. You.

  Further, when producing a pigment dispersion for each pigment, a different pigment dispersion resin may be selected for each pigment dispersion, or the same pigment dispersion resin may be used, but from the viewpoint of storage stability of the ink. It is preferable to use the same pigment dispersion resin.

<(2) Preparation of ink>
Next, a water-soluble organic solvent such as a diol-based solvent (A-1), water, and, if necessary, the above-mentioned binder resin, surfactant, and / or other additives are added to the pigment dispersion. Stir and mix the resulting mixture. In addition, you may stir and mix, heating a mixture in the range of 40-100 degreeC as needed.

<(3) Removal of coarse particles>
The coarse particles contained in the above mixture are removed by a method such as filtration or centrifugation to obtain a magenta ink for inkjet. A known method can be appropriately used as a method of the filtration separation. The filter opening diameter is not particularly limited as long as coarse particles and dust can be removed, but is preferably 0.3 to 5 μm, more preferably 0.5 to 3 μm. When performing filtration, a single type of filter may be used, or a plurality of types may be used in combination.

<Poorly absorbable substrate>
The ink of the embodiment of the present invention can be suitably used not only for easily absorbable base materials such as plain paper or special paper, but also for poorly absorbable base materials. The “poorly absorbable substrate” in the embodiment of the present invention refers to a substrate that does not absorb water or has a low absorption rate, and is described below by the Bristow method (J. TAPPI paper pulp test method No. 51-). 87) represents a substrate having an absorption coefficient for water of 0 to 0.6 ml / m ² msec ^1/2 measured by 87). Specific examples include, but are not limited to, paper base materials such as coated papers, art papers, finely coated papers, cast coated papers, and plastic base materials such as polyvinyl chloride sheets, PET films, and PP films. It is not done.

  Further, the substrate used in the embodiment of the present invention may have a smooth surface of the printing substrate, may have irregularities, or may be transparent, translucent, or opaque. Good. Further, two or more of these printing base materials may be bonded to each other. Further, a release adhesive layer or the like may be provided on the side opposite to the printing surface, or an adhesive layer may be provided on the printing surface after printing.

The above absorption coefficient can be measured by using, for example, an automatic scanning liquid absorption meter manufactured by Kumagai Riki Kogyo Co., Ltd. Specifically, using the above apparatus and water, the liquid absorption amount (ml / m ² ) of water obtained during the contact time of 100 to 1,000 milliseconds and the square root of the contact time (msec ^1/2 ) The gradient of a straight line obtained by the least squares method is determined as the absorption coefficient.

<Production method of printed matter>
As a method of manufacturing a printed material using the magenta ink for ink jet or the ink set according to the embodiment of the present invention, a method of ejecting ink from an ink jet head and attaching ink droplets onto a printing substrate is used. As described above, a poorly absorbable substrate can be suitably used as the printing substrate.

  Further, it is preferable to apply thermal energy to the printing substrate for drying the ink droplets after the ink droplets are deposited on the printing substrate. The method of applying heat energy is not particularly limited, and examples thereof include a heat drying method, a hot air drying method, an infrared drying method, a microwave drying method, and a drum drying method. These drying methods may be used alone or in combination. For example, by using both the heat drying method and the hot air drying method, the ink can be dried more quickly than when each is used alone.

  In addition, when the magenta ink for inkjet of the embodiment of the present invention is used as an ink set in combination with a cyan ink and a yellow ink, after printing each ink included in the ink set, each time, even if heat energy is applied, Alternatively, after printing all the inks, heat energy may be applied collectively.

<Inkjet head>
In general, as the design resolution of an ink jet head increases, the nozzle diameter decreases. As a result, the amount of ink droplets ejected from the nozzles also decreases, so that the delicateness of the printed matter increases and the image quality improves. In particular, by using an inkjet head having a design resolution of 600 dpi or more, a printed matter having excellent image quality can be produced. On the other hand, in order to set the design resolution of the ink jet head to 600 dpi or more, it is preferable that the distance between adjacent nozzles is set to about 42 μm or less, and the nozzle diameter is reduced accordingly. However, as the nozzle diameter is reduced, the ink is more susceptible to drying and the precipitation of components such as pigments, and ejection failure is more likely to occur. Further, since the amount of ink droplets applied to the base material is reduced, it is preferable to use an ink having excellent color developability, sharpness, and color reproducibility even if the amount is small.

  In contrast to the above, the magenta ink of the embodiment of the present invention can provide a high-quality image having high color development and high clarity even with a poorly absorbable substrate, and also has excellent ejection stability and drying properties. Excellent, and when used as an ink set, high color reproducibility can be realized, so that it can be suitably used even for an ink jet head having a large design resolution, that is, a small nozzle diameter.

  The magenta ink according to the embodiment of the present invention, and the nozzle diameter of the inkjet head used in the method for producing a printed material using the ink set containing the magenta ink is preferably 10 to 30 μm, more preferably 12 to 25 μm. And particularly preferably 15 to 20 μm. By using an ink jet head having a smaller nozzle diameter, the discharge amount of ink droplets can be reduced, and higher quality printed matter can be manufactured. The design resolution of the inkjet head is preferably from 600 to 1,600 dpi, and more preferably from 1,200 to 1,600 dpi.

<Spectral reflectance of ink-coated product>
The magenta ink of the embodiment of the present invention preferably has a spectral reflectance of 10% or less in a wavelength region of 480 to 580 nm in a coated product having a wet film thickness of 6 μm, which is formed on a printing substrate. As described above, in the magenta ink of the embodiment of the present invention, the balance of the azo pigment, the diol-based solvent (A-1), and other materials is considered to be an important factor. It has been found that the width of the prescription for obtaining a suitable balance varies depending on the type of the compound. Although the detailed factors are unknown, a part of the azo pigment agglomerates in the ink, thereby disturbing the balance of the content. It is considered that reproducibility cannot be sufficiently expressed. In addition, when printing on a poorly absorbable substrate, it is considered that quality deterioration such as color development and color reproducibility is likely to occur particularly.

  If the aggregation is severe, the presence or absence of aggregation can be determined by, for example, measuring the particle size distribution of the ink.However, if the pigment is partially agglomerated to some extent, it may not be confirmed by measuring the particle size distribution of the ink. . Therefore, as a result of intensive studies by the present inventors, it has been found that by measuring the spectral reflectance in the wavelength region of 480 to 580 nm, even a small amount of aggregation can be significantly judged. This is because the component volatilized from the ink upon drying hardly affects the reflectance in the above wavelength range, so the value changes little between the coated product obtained by wet coating and the coated product after drying. It is due to not doing. The balance with the diol-based solvent (A-1) is maintained by suppressing the spectral reflectance of the coating material having a wet film thickness of 6 μm formed on the printing base material to 10% or less in a wavelength region of 480 to 580 nm. The range of possible formulations can be widened, and a magenta ink capable of expressing the excellent color developing property and color reproducibility inherently possessed by the azo pigment can be obtained. That is, it is possible to widen the range of selection of the types and contents of the components contained in the ink.

  A specific example of the method for measuring the spectral reflectance in the embodiment of the present invention is K Control Coater K202 manufactured by Matsuo Sangyo Co., Ltd. After applying the magenta ink of the embodiment of the present invention to the printing base material using No. 1 and drying it in an air oven at 60 ° C. for 3 minutes to produce a coated product, the spectral reflectance on the coated product is There is a method of measuring using i1Pro2 manufactured by X-rite. In the measurement of the spectral reflectance, it is particularly preferable that the spectral reflectance is 10% or less in all the regions in the wavelength range of 480 to 580 nm at 10 nm intervals.

As the above-mentioned coated product, for example, an ink jet printer may be used to adjust the ink ejection amount so that the wet film thickness becomes 6 ± 0.3 μm, and a solid image printed on a printing substrate may be used. Further, as a printing base material, for example, OK Topcoat + (US basis weight 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd. can be used.

  For the same pigment, as a method for keeping the spectral reflectance in the wavelength range of 480 to 580 nm within the above range, for example, adjusting the type and the mixing ratio of the pigment used together, the dispersion time in the dispersion step and the pulverization media of a disperser Adjustment, use of the above-mentioned pigment dispersion resin and adjustment of the kind and amount thereof, and use of a dispersing aid such as a pigment derivative in combination.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following description, “parts” and “%” represent “parts by mass” and “% by mass”, respectively, unless otherwise specified.

  In the examples, the weight average molecular weight is a value in terms of polystyrene measured using a TSKgel column (manufactured by Tosoh Corporation) and GPC (manufactured by Tosoh Corporation, HLC-8120GPC) equipped with an RI detector using THF as a developing solvent. It is. The acid value (mgKOH / g) is a value obtained by titration with a KOH solution in an ethanol / toluene mixed solvent using an automatic potentiometric titrator AT-610 manufactured by Kyoto Electronics Industry Co., Ltd. The glass transition temperature (° C.) is a value obtained by reading the endothermic peak temperature of a chart obtained at a temperature rising condition of 5 ° C./min using “Differential Scanning Calorimeter DSC-60PLUS” manufactured by Shimadzu Corporation.

<I. Manufacture of ink materials>
<Production Example of Pigment Dispersion Resin 1>
A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 93.4 parts of butanol and replaced with nitrogen gas. The reaction vessel was heated to 110 ° C., and 30 parts of acrylic acid, 40 parts of methyl methacrylate, 30 parts of stearyl methacrylate, and 6 parts of V-601 (manufactured by Wako Pure Chemical Industries) as a polymerization initiator were heated as the polymerizable monomer. The mixture was dropped over 2 hours to carry out a polymerization reaction. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, 0.6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour to obtain a dispersion resin 1 solution. Was. Furthermore, after cooling to room temperature, 37.1 parts of dimethylaminoethanol was added for neutralization, 100 parts of water was added, and the mixture was stirred. Thereafter, the mixture was heated to 100 ° C. or higher, butanol was azeotropically distilled with water to distill butanol, and the solid content was adjusted to 50%. As a result, an aqueous solution (a solution containing a solvent containing water and components dispersed and / or dissolved in the solvent) having a solid content of 50% of the pigment dispersion resin 1 was obtained. In addition, the pigment dispersion resin 1 was water-soluble.

<Production Examples of Pigment Dispersion Resins 2 to 5>
Except that the monomers shown in Table 1 were used as the polymerizable monomers, an aqueous solution having a solid content of 50% of pigment dispersion resins 2 to 5 was obtained in the same manner as in pigment dispersion resin 1. The pigment-dispersed resins 2 to 5 were all water-soluble.

The abbreviations described in Table 1 are as follows.
-St: styrene-AA: acrylic acid-MMA: methyl methacrylate-2EHA: 2-ethylhexyl acrylate-STMA: stearyl methacrylate

<Production Example of Methyl Ethyl Ketone Solution of Pigment Dispersion Resins 6 to 7>
A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was charged with 95 parts of methyl ethyl ketone and purged with nitrogen gas. The inside of the reaction vessel was heated to 80 ° C., and 70 parts of styrene as a polymerizable monomer, 5 parts of acrylic acid, 10 parts of methyl methacrylate, 15 parts of polypropylene glycol methacrylate (Blenmer PP-500 manufactured by NOF CORPORATION), and a polymerization initiator A mixture of 3.5 parts of V-65 (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over 3 hours to carry out a polymerization reaction. After completion of the dropwise addition, the mixture was reacted at 80 ° C. for 1 hour, 0.7 parts of V-65 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 80 ° C. for 4 hours. Obtained. Thereafter, 25 parts of methyl ethyl ketone was added, the reaction system was cooled to room temperature, the mixed solution was taken out from the reaction vessel, and adjusted with methyl ethyl ketone so that the solid content became 30%. Min 30%). Further, as shown in Table 2 below, a methyl ethyl ketone solution (solid content: 30%) of the pigment dispersion resin 7 was prepared in the same manner as in the case of the pigment dispersion resin 6, except that the type and amount of the polymerizable monomer were changed. Got. In addition, each of the pigment dispersion resins 6 and 7 was insoluble in water.

Among the abbreviations described in Table 2, those not described in Table 1 are as follows.
-VMA: behenyl methacrylate-PP500: polypropylene glycol methacrylate (Blenmer PP-500 manufactured by NOF Corporation)

<Examples of production of binder resins 1 to 8>
An aqueous solution of binder resins 1 to 8 having a solid content of 50% was obtained in the same manner as in pigment dispersion resin 1 except that the monomers shown in Table 3 were used as the binder resin used in the examples. Then, 25 parts of water was added to 100 parts of the obtained aqueous solution of the binder resins 1 to 8, respectively, and mixed well to adjust the solid content of the aqueous solution of the binder resins 1 to 8 to 40%. . The binder resins 1 to 8 were all water-soluble.

Among the abbreviations described in Table 3, those not described in Tables 1 and 2 are as follows.
• αMSt: α-methylstyrene • MAA: methacrylic acid • BMA: butyl methacrylate

<Other binder resins>
Further, the following styrene acrylic resin fine particles were used as the binder resin. In the following, a dispersion liquid having a solid content adjusted to 40% using water was used.
-Joncryl 537J: manufactured by BASF, acid value: 40 mgKOH / g, Tg: 49 ° C
-Neoacryl A-1091: manufactured by DSM Coating Resins, acid value: 34 mgKOH / g, Tg: 98 ° C
-Neoacryl A-1092: manufactured by DSM Coating Resins, acid value: 24 mgKOH / g, Tg: 9 ° C

<Production Example of Magenta Pigment Dispersion 1>
C. I. Pigment Red 150, 10 parts of C.I. I. Pigment Red 48: 3, 10 parts of an aqueous solution of the pigment dispersion resin 1, 10 parts of water, and 70 parts of water are thoroughly mixed with a disper (stirrer), and then zirconia beads having a diameter of 0.5 mm and 1,800 g are mixed. This dispersion was carried out using a 0.6 L dyno mill filled with, and magenta pigment dispersion liquid 1 (MB1) was obtained.

<Production Examples of Magenta Pigment Dispersions 2 to 53, 56, 57, 60, 61>
Pigment dispersion was performed in the same manner as in magenta pigment dispersion 1 except that the raw materials shown in Table 4 were used, and magenta pigment dispersions 2 to 53, 56, 57, 60, and 61 (MB2 to 53, 56, 57, 60, 61).

<Production Example of Magenta Pigment Dispersions 54, 55, 58, 59>
To a mixing vessel equipped with a stirrer, 16.7 parts of a methyl ethyl ketone solution (solid content concentration: 30%) of the pigment dispersion resin 6 and 13.1 parts of methyl ethyl ketone were added, and then, with stirring, 50 parts of water and dimethyl 0.2 parts of aminoethanol were added, and the mixture was further stirred for 30 minutes. Thereafter, C.I. I. Pigment Red 150, 18 parts of C.I. I. Pigment Red 48: 3 (2 parts) was added, mixed well with a disper (stirrer), and then fully dispersed using a 0.6-L Dynomill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. . Next, the obtained dispersion was taken out, and after adding 15 parts of water, methyl ethyl ketone was distilled off under reduced pressure using an evaporator. Thereafter, the pigment concentration was adjusted to 20% to obtain a magenta pigment dispersion liquid 54 (MB54).
Further, the same operation as for the magenta pigment dispersion liquid 54 was performed except that the raw materials shown in Table 4 were used, and magenta pigment dispersion liquids 55, 58, and 59 (MB55, 58, and 59) were obtained.

The abbreviations described in Table 4 are as follows.
・ P. R. 150: C.I. I. Pigment Red 150
・ P. R. 146: C.I. I. Pigment Red 146
・ P. R. 147: C.I. I. Pigment Red 147
・ P. R. 170: C.I. I. Pigment Red 170
・ P. R. 266: C.I. I. Pigment Red 266
・ P. R. 269: C.I. I. Pigment Red 269
・ P. R. 1: C.I. I. Pigment Red 1
・ P. R. 166: C.I. I. Pigment Red 166
・ P. R. 48: 1: C.I. I. Pigment Red 48: 1
・ P. R. 48: 3: C.I. I. Pigment Red 48: 3
・ P. R. 122: C.I. I. Pigment Red 122
・ P. R. 202: C.I. I. Pigment Red 202
・ P. R. 209: C.I. I. Pigment Red 209
-QCD solid solution: C.I. I. Pigment Red 202 and C.I. I. Pigment Violet 19 (Cinquasia Red K4330 manufactured by BASF)

<Production Examples of Yellow Pigment Dispersions 1 to 3>
C.I. I. Pigment Yellow 74, 10 parts of an aqueous solution of Pigment Dispersion Resin 1, and 70 parts of water were mixed, predispersed with a disper, and filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was carried out using a 6 L Dyno mill to obtain a yellow pigment dispersion liquid 1.
Each of the pigments is C.I. I. Pigment Yellow 14 or C.I. I. Pigment dispersion was carried out in the same manner as in Yellow pigment dispersion 1 except that Pigment yellow 120 was used, to obtain Yellow pigment dispersions 2 and 3.

<Production Example of Cyan Pigment Dispersion 1>
C.I. I. Pigment Blue 15: 3, 20 parts of an aqueous solution of Pigment Dispersion Resin 1, and 70 parts of water are mixed, predispersed by a disper, and filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was carried out using a 0.6 L Dyno mill to obtain a cyan pigment dispersion liquid 1.

<II. Production and evaluation of magenta ink>
<Production example of magenta ink 1 (M1)>
10 parts of magenta pigment dispersion 1 (MB1), 15 parts of propylene glycol, 5 parts of diethylene glycol monobutyl ether, 1 part of Surfynol 440, and 10 parts of an aqueous solution of binder resin 1 (4 parts as solid content), in that order Then, water was added so that the total amount of the ink became 100 parts. The mixture was stirred with a disper until the mixture was sufficiently uniform, and then filtered through a membrane filter having a pore size of 1 μm to remove coarse particles that could cause head clogging, thereby producing a magenta ink 1 (M1).

<Production Example of Magenta Inks 2 to 123 (M2 to 123)>
Magenta inks 2 to 123 (M2 to M123) were produced in the same manner as in the production example of magenta ink 1, except that the raw materials described in Tables 5 and 6 were used.

The abbreviations described in Tables 5 and 6 and the materials used are as follows.
・ EG: Ethylene glycol (boiling point: 197 ° C)
-DEG: diethylene glycol (boiling point: 244 ° C)
・ PG: Propylene glycol (boiling point: 188 ° C)
・ DPG: dipropylene glycol (boiling point: 231 ° C.)
・ TEG: Triethylene glycol (boiling point: 288 ° C)
・ TPG: Tripropylene glycol (boiling point: 273 ° C)
2Py: 2-pyrrolidone (boiling point: 245 ° C)
NMP: N-methylpyrrolidone (boiling point: 202 ° C)
-1,2-BD: 1,2-butanediol (boiling point: 191 ° C, surface tension: 32 mN / m, HLB value: 7.6)
-1,2-HD: 1,2-hexanediol (boiling point: 224 ° C, surface tension: 26 mN / m, HLB value: 5.8)
-DPM: dipropylene glycol monomethyl ether (boiling point: 188 ° C, surface tension: 27 mN / m, HLB value: 2.3)
-BDG: diethylene glycol monobutyl ether (boiling point: 230 ° C, surface tension: 28 mN / m, HLB value: 13.0)
Gly: glycerin (boiling point: 290 ° C., surface tension: 62 mN / m, HLB value: 11.1)
-Surfynol 104: acetylene-based surfactant (manufactured by Nissin Chemical Industry Co., Ltd., HLB: 3.0)
-Surfynol 440: an acetylene-based surfactant having an ethylene oxide group (manufactured by Nissin Chemical Co., Ltd., HLB: 9.9)
-Surfynol 485: an acetylene-based surfactant having an ethylene oxide group (manufactured by Nissin Chemical Co., Ltd., HLB: 17.5)
Emarex 703: In formula (2), R is a lauryl group, and a glycol ether surfactant having three ethylene oxide groups (manufactured by Nippon Emulsion, HLB: 9.4)
Emarex 630: In the formula (2), R is a stearyl group and a glycol ether surfactant having 30 ethylene oxide groups (manufactured by Nippon Emulsion Co., Ltd., HLB: 16.7)
Emarex 750: In formula (2), R is a lauryl group and a glycol ether surfactant having 50 ethylene oxide groups (manufactured by Nippon Emulsion Co., Ltd., HLB: 18.6)
Nonionic K-2100W: In the formula (2), R is a lauryl group, and a glycol ether surfactant having 100 ethylene oxide groups (manufactured by Nippon Emulsion Co., Ltd., HLB: 19.3)
-TegoWet280: siloxane-based surfactant having an ethylene oxide group (HLB: 3.5, manufactured by Evonik Japan)

<Examples 1 to 114, Comparative Examples 1 to 9>
The magenta inks 1 to 123 (M1 to M123) produced above were evaluated as follows. The obtained evaluation results were as shown in Tables 5 and 6.

<Evaluation 1: Evaluation of storage stability of magenta ink>
The viscosities of the magenta inks M1 to M123 were measured using an E-type viscometer (TVE-20L manufactured by Toki Sangyo Co., Ltd.) under the conditions of 25 ° C. and 50 rpm. These inks were sealed in a closed container and stored in a 70 ° C. thermostat. After a lapse of a predetermined period, the viscosity of the ink in the closed container taken out of the thermostat was measured, and the storage stability was evaluated by calculating the viscosity change rate of the ink before and after storage. The evaluation criteria were as described below, and the AA, A, and B evaluations were regarded as practically usable areas.
AA: Change in viscosity after storage for 4 weeks was less than ± 5% A: Change in viscosity after storage for 2 weeks was less than ± 5%, but change in viscosity after storage for 4 weeks was ± 5% B: The rate of change in viscosity after storage for one week was less than ± 5%, but the rate of change in viscosity after storage for two weeks was ± 5% or more C: The rate of change in viscosity after storage for one week Was ± 5% or more

<Evaluation 2: Evaluation of ejection stability of magenta ink>
Magenta inks M1 to M123 were filled in an inkjet discharge device equipped with an Kyocera inkjet head (KJ4B-QA model, design resolution 600 dpi). After confirming that there was no nozzle missing (a phenomenon in which ink was not ejected from the nozzle), the inkjet ejecting apparatus was allowed to stand by for a certain period of time in an environment of 25 ° C. After a lapse of a predetermined time, a nozzle check pattern was printed, and the number of missing nozzles was visually counted to evaluate the ejection stability. The evaluation criteria were as described below, and the AA, A, and B evaluations were regarded as practically usable areas.
AA: No nozzle missing even when printing after waiting for 4 hours A: No nozzle missing even when printing after waiting for 2 hours, but nozzle missing when printing after waiting for 4 hours One or more nozzles were generated. B: No nozzle missing occurred even after printing after waiting for one hour. However, when printing was performed after waiting for two hours, one or more nozzle missing occurred. C: One hour. When printing after waiting, one or more nozzles were missing.

<Evaluation 3: Evaluation of white spots on magenta ink printed matter>
Magenta inks M1 to M123 were filled in an inkjet discharge device equipped with an Kyocera inkjet head (KJ4B-QA model, design resolution 600 dpi). Then, under a printing condition of a frequency of 20 kHz and 600 × 600 dpi, a solid printing at a printing rate of 100% was performed on OK Topcoat + (US basis weight: 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd. It was dried for 3 minutes in an oven to produce a solid print. Then, the obtained solid printed matter was visually checked with a loupe and the white spots were evaluated. The evaluation criteria were as follows, and the A and B evaluations were defined as a practically usable area.
A: No white spots were observed on the loupe and visually B: White spots were slightly observed on the loupe, but no white spots were visually observed C: Clear white spots were visually observed

<Evaluation 4: Evaluation of density of magenta ink print>
The density (OD value) of the solid printed matter having a printing rate of 100% produced in the evaluation of white spots was measured. The evaluation criteria were as described below, and the AA, A, and B evaluations were regarded as practically usable areas. In addition, "eXact standard" manufactured by X-rite was used for measuring the concentration. The measurement conditions were: observation light source: D50, observation field of view: 2 °, density: status E, white standard: Abs, measurement mode: M0.
AA: OD value was 1.6 or more A: OD value was 1.5 or more and less than 1.6 B: OD value was 1.4 or more and less than 1.5 C: OD value was 1 Was less than 4.

<Evaluation 5: Evaluation of saturation of magenta ink printed matter>
The CIE-Lab value of the solid printed matter having a printing rate of 100% produced in the evaluation of white spots was measured using the same measuring instrument ("XACT Standard" manufactured by X-rite) and the same measurement conditions as those used in the evaluation of the density. (L * a * b * values) were measured. Then, the saturation C * (= (a * ² + b * ² ) ^1/2 ) was calculated from the obtained a * value and b * value. The evaluation criteria were as described below, and the AA, A, and B evaluations were regarded as practically usable areas.
AA: C * value was 78 or more A: C * value was 76 or more and less than 78 B: C * value was 74 or more and less than 76 C: C * value was less than 74

<Evaluation 6: Evaluation of drying property of magenta ink printed matter>
The same printing conditions (printing conditions) as in the evaluation of white spots and solid printing at a printing rate of 100% were performed using a printing substrate. After the printing, the printed matter was put into an air oven at 60 ° C., and the dryness of the printed matter was evaluated by touching the printed matter with a finger every 15 seconds. The evaluation criteria were as follows, and the A and B evaluations were defined as a practically usable area.
A: The ink did not adhere to the finger even when touched 15 seconds after the oven was put.
B: The ink adhered to the finger 15 seconds after the oven was charged, but did not adhere after 30 seconds. C: The ink was adhered to the finger even 30 seconds after the oven was charged.

<III. Manufacture and evaluation of ink sets>
<Production of yellow inks 1 to 15 (Y1 to 15)>
20 parts of the yellow pigment dispersion 1, 25 parts of propylene glycol, 5 parts of diethylene glycol monobutyl ether, 1 part of Surfynol 440, and 10 parts of an aqueous solution of the binder resin 1 (4 parts as solid content) are sequentially placed in a mixing vessel. After the introduction, water was added so that the total amount of the ink became 100 parts. The mixture was stirred by a disper until the mixture became sufficiently uniform, and then filtered through a membrane filter having a pore size of 1 μm to remove coarse particles that could cause head clogging, thereby producing a yellow ink 1 (Y1).
Also, yellow inks 2 to 15 (Y2 to Y15) were produced in the same manner as in the production example of yellow ink 1, except that the raw materials shown in Table 7 were used.

<Production of cyan inks 1 to 13 (C1 to 13)>
20 parts of the cyan pigment dispersion 1, 25 parts of propylene glycol, 5 parts of diethylene glycol monobutyl ether, 1 part of Surfynol 440, and 10 parts of an aqueous solution of the binder resin 1 (4 parts as solid content) are sequentially charged into a mixing vessel. After that, water was added so that the total amount of the ink became 100 parts. The mixture was stirred by a disper until the mixture was sufficiently uniform, and then filtered through a membrane filter having a pore size of 1 μm to remove coarse particles causing clogging of the head, thereby producing a cyan ink 1 (C1).
Cyan inks 2 to 13 (C2 to C13) were produced in the same manner as in the production example of cyan ink 1 except that the raw materials shown in Table 8 were used.

<Examples 115 to 139, Comparative Examples 10 to 11>
The magenta ink, yellow ink, and cyan ink produced above were used in combinations (ink sets) shown in Table 9, and the following evaluations were made. The obtained evaluation results were as shown in Table 9.

<Evaluation 7: Evaluation of color mixture bleeding of inkjet ink set>
The ink combinations described in Table 9 were used as ink sets, and the ink sets were filled in an inkjet discharge device equipped with three Kyocera inkjet heads (KJ4B-QA model, design resolution 600 dpi). Next, under the printing conditions of a frequency of 30 kHz and 600 × 600 dpi, the color chart image (cyan, magenta, and yellow was multiplied by a printing rate of 10%, respectively) by discharging ink onto the hardly absorbable substrate. The image on which the patches were arranged) was printed, and dried using an air oven at 60 ° C. for 3 minutes. Note that drying was not performed for each color, but all the inks were printed and then put into an air oven to dry all three colors at once.
Then, in the obtained printed matter, a portion where the total printing ratio (total of the printing ratio of each color) is 210% (the printing ratio of each color is 70%) is confirmed by a loupe and a visual check. And evaluation of color mixture bleeding. The evaluation criteria were as follows, and the A and B evaluations were defined as a practically usable area. As the poorly absorbable base material, OK Topcoat + (US basis weight: 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd., and FOR # 20 (biaxially stretched PP film, thickness: 20 μm) manufactured by Futamura Chemical Co., Ltd. )It was used.
A: No bleeding was observed in the loupe and visually B: Slight bleeding was observed in the loupe, but no bleeding was visually observed C: The bleeding was clearly observed visually

<Evaluation 8: Evaluation of color reproducibility of inkjet ink set>
Using the combinations of the inks described in Table 9 as ink sets, two types of ink jet heads shown below were filled in an ink jet discharge device equipped with three each. After filling, the ink is discharged onto the OK Topcoat + (US basis weight: 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd. at the following resolution, and solid patch images (cyan, magenta, yellow primary color solid patches) (Printing rate 100%), and printing of a secondary color solid patch (printing rate 200%) arrayed by combining two of the three colors, and printing using a 60 ° C. air oven. Dried for minutes.
Then, the CIE-Lab value (L * a * b * value) of each solid patch was measured using the same measuring device ("Xext standard" manufactured by X-rite) used for the evaluation of the above-mentioned concentration, and a Japanese color sheet was measured. The color reproducibility was evaluated by comparing with the L * a * b * values of the primary color solid and the secondary color solid specified for the leaf printing 2011. The evaluation criteria were as described below, and the AA, A, and B evaluations were regarded as practically usable areas.
AA: Color reproduction area equal to or higher than Japan color A: Color reproduction area equivalent to Japan color B: Color reproduction area slightly less than Japan color C: Color much smaller than Japan color Reproduction area

The inkjet heads used in the above Evaluation 8 are as follows.
Head A: Kyocera inkjet head (KJ4B-QA model, design resolution 600 dpi, nozzle diameter: 25 μm, printing resolution 600 × 600 dpi)
Head B: Kyocera inkjet head (KJ4B-1200 model, design resolution 1200 dpi, nozzle diameter: 20 μm, printing resolution 1200 × 1200 dpi)

<Evaluation 9: Evaluation of sharpness of printed matter produced using inkjet ink set>
The ink combinations described in Table 9 were used as ink sets, and the ink sets were filled in an inkjet discharge device equipped with three Kyocera inkjet heads (KJ4B-QA model, design resolution 600 dpi). Then, under the printing conditions of a frequency of 30 kHz and 600 × 600 dpi, the ink is ejected onto the hardly-absorbable base material to obtain a natural image N5 (bicycle) of JIS X9201 high-definition color digital standard image data (CMYK / SCID). Printing was performed and dried for 3 minutes using a 60 ° C. air oven. Note that drying was not performed for each color, but all the inks were printed and then put into an air oven to dry all three colors at once.
Then, the obtained printed matter was visually observed, and the relative clearness was compared to evaluate the sharpness. The evaluation criteria were as follows, and the A and B evaluations were defined as a practically usable area. As the poorly absorbable base material, OK Topcoat + (US basis weight: 104.7 g / m ² ) manufactured by Oji Paper Co., Ltd., and FOR # 20 (biaxially stretched PP film, thickness: 20 μm) manufactured by Futamura Chemical Co., Ltd. )It was used.
A: The sharpness was superior to the printed matter of Example 131. B: The sharpness was almost the same as the printed matter of Example 131. C: The sharpness was inferior to the printed matter of Example 131.

  From Examples 1 to 114 shown in Table 5, by using the magenta ink for inkjet according to the embodiment of the present invention, even with a poorly-absorbable substrate, there is no white spots, high color development and high sharpness. It has been found that a high-quality image can be obtained, and that the ink has excellent storage stability, ejection stability, and drying properties. Further, from Examples 115 to 139 shown in Table 9, by using the ink set including the magenta ink for inkjet according to the embodiment of the present invention, when the design resolution of the inkjet head is large, and / or like a PP film. It has been found that even when a low-absorbency substrate is used, a printed matter having high color reproducibility and clarity and free from color mixture bleeding can be obtained.

  On the other hand, Comparative Example 1 shown in Table 6 is a system in which the content of the azo pigment was less than 35% by mass of the total amount of the pigment, and Comparative Example 3 in which the azo pigment was not contained, together with the color development of the printed matter. The result was inferiority and sharpness. In the ink sets containing these inks (Comparative Examples 10 to 11 in Table 9), poor color reproducibility of the printed matter was also confirmed. Conversely, in Comparative Example 2 in which the pigment contains only one type of azo pigment, the color development and sharpness of the printed matter are good, but the ejection is considered to be caused by the dissolution and / or dispersion of the azo pigment. Deterioration of stability was confirmed. Similarly, Comparative Example 4 in which the content of the azo pigment was more than 8% by mass also resulted in poor ejection stability.

  Comparative Examples 5 to 6 are systems in which the molar amount of the diol-based solvent (A-1) is not 5 to 250 times the molar amount of the azo pigment. Among them, in the system in which the content of the diol-based solvent (A-1) was too small relative to the content of the azo pigment (Comparative Example 5), it was confirmed that the coloring property of the printed matter and the ejection stability were deteriorated. . It is considered that the protection of the azo pigment was insufficient. On the other hand, even in a system in which the content of the diol solvent (A-1) was too large relative to the content of the azo pigment (Comparative Example 6), the color development of the printed matter was inferior. Although the detailed reason is unknown, the result suggests that an excessive amount of the diol-based solvent (A-1) adversely affects the color developability of the printed matter.

  Comparative Example 7 is a system containing an excess amount of a diol-based solvent (A-2), and Comparative Example 8 is a system containing an excess amount of a cyclic amide-based solvent, resulting in inferior discharge stability and storage stability, respectively. . Further, in Comparative Example 9 containing no surfactant, white spots, which are considered to be caused by insufficient wetting and spreading on the printing substrate, were confirmed.

  The above results indicate that the magenta ink for inkjet having the configuration of the embodiment of the present invention, and the ink set containing the magenta ink have storage stability, ejection stability, color development of printed matter, sharpness, and color reproducibility. This shows that all of the printing quality and the drying property for the poorly-absorbable substrate can be at the same time.

  The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2018-109736 filed on June 7, 2018, the entire disclosure of which is incorporated herein by reference.

Claims (14)

A magenta ink for inkjet containing two or more pigments, a water-soluble organic solvent (A), a surfactant, and water,
The two or more pigments contain an azo pigment,
The content of the azo pigment is 0.5 to 8% by mass based on the total amount of the magenta ink for inkjet, and 35 to 100% by mass based on the total amount of the pigment,
The water-soluble organic solvent (A) is a diol-based solvent represented by the following formula (1), wherein n is 1 and / or 2; Contains 5-250 times the amount of
In the water-soluble organic solvent (A), the diol-based solvent (A-2) in which n is 3 and / or 4 among the diol-based solvents represented by the following formula (1) is contained in the diol-based solvent. 0.1 times or less the molar amount of the solvent (A-1),
The magenta ink for inkjet, wherein the content of the cyclic amide solvent in the water-soluble organic solvent (A) is 4.5% by mass or less based on the total amount of the magenta ink for inkjet.

HO- (AO) n-H (1)

(In the formula (1), AO represents an ethylene oxide group or a propylene oxide group, and n represents an integer of 1 to 4.)   The magenta ink for inkjet according to claim 1, wherein the azo pigment includes a naphthol AS pigment and / or a β-oxynaphthoic acid-based lake pigment.   The azo pigment includes a naphthol AS pigment, and a β-oxynaphthoic acid lake, and the β-oxynaphthoic acid lake is based on the total amount of the naphthol AS pigment and the β-oxynaphthoic acid lake pigment. The magenta ink for inkjet according to claim 2, wherein the content of the pigment is 50 to 99% by mass.   The naphthol AS pigment is C.I. I. The magenta ink for inkjet according to claim 2, comprising Pigment Red 150.   The β-oxynaphthoic acid-based lake pigment is C.I. I. The magenta ink for inkjet according to any one of claims 2 to 4, comprising Pigment Red 48: 3.   The magenta ink for inkjet according to any one of claims 1 to 5, wherein the two or more types of pigments further include a quinacridone pigment and / or a solid solution pigment containing a quinacridone pigment. The azo pigment includes a naphthol AS pigment,
The magenta ink for inkjet according to any one of claims 2 to 6, wherein the content of the azo pigment is more than 50% by mass and 99% by mass or less based on the total amount of the two or more types of pigments.   The magenta ink for inkjet according to any one of claims 1 to 7, further comprising a binder resin, wherein the glass transition temperature (Tg) of the binder resin is 40 to 120 ° C.   The magenta ink for inkjet according to any one of claims 1 to 8, wherein a spectral reflectance of a coated product having a wet film thickness of 6 µm produced on a printing substrate is 10% or less in a wavelength region of 480 to 580 nm. An inkjet ink set including at least a cyan ink, a yellow ink, and a magenta ink,
The cyan ink and the yellow ink contain the diol-based solvent (A-1),
An ink set, wherein the magenta ink is the magenta ink for inkjet according to any one of claims 1 to 9.   The molar amount of the diol-based solvent (A-1) contained in each of the magenta ink, the cyan ink, and the yellow ink is 5 to 250 times the molar amount of the azo pigment in the magenta ink. The ink set according to claim 10, which is provided.   The magenta ink for inkjet according to any one of claims 1 to 9, or the ink set according to claim 10 or 11, which is ejected from an inkjet head to adhere ink droplets to a poorly-absorbable substrate. Production method.   The method according to claim 12, wherein the nozzle diameter of the inkjet head is 10 to 30 m.   An inkjet printed matter obtained by printing the magenta ink for inkjet according to any one of claims 1 to 9 or the ink set according to claim 10 or 11 on a poorly absorbent substrate.